FIELD TRIP EVENTS

In recent years Gem-A has run a number of Field Trips to introduce our Members to the wider world of gemmology.

Starting in 2013, Gem-A reintroduced our Field Trip programme to bring our global network of Members closer together and create social and business connections across the globe. With our recent field trips to Idar-Oberstein, the Association has initiated a reinvigorated attitude to providing first-class experiences created for and by our members. 

To find out more about our upcomming Field Trip events, or to contact us and suggest a trip or invite Gem-A Members to visit you, click the link below. 

Event type

 

Fossicking in the Outback

Carmen Garcia-Carballido FGA DGA L.Geology MSc. EurGeol travelled to the southern hemisphere to find out more about the opals and sapphires of eastern Australia.

To test the skills acquired in two years training as a gemmologist with Gem-A, my husband planned a three week field trip to the sapphire and opal fields of eastern Australia.

We flew from Aberdeen to Sydney, hired a motorhome and headed into the outback of New South Wales (NSW) and Queensland. However, cyclone Debbie making landfall on the coast put paid to our plan to visit a gem dealer in Yepoon and check out the Marlborough Chrysoprase. To keep safe we stayed inland, driving 4,500 km in 13 days and camping at a different site every night.

Map of Australia showing key sapphire and opal locations and the field trip itinery. Image by Peter Scott-Wilson.

Two days from Sydney, our first gem field was Glenn Innes where we tried fossicking for the first time. A petrol station sold us a ‘bucket of dirt’ and rented sieves for AUS $20. Washing the dirt off, we found our first sapphires and zircons. We admired Robert Cook's collection of locally mined parti-colour sapphires that he cuts in his shop at the Visitor Information Centre. After some purchases, my husband had to drag me out of Robert’s shop.

60 km west at Inverell, we met Jack Wilson, who owns a longstanding sapphire mine and his wife Dallas, who designs lovely jewellery with blue sapphires from his mine. I bought some untreated rough blue sapphires with the idea of learning to cut them myself. Jack explained the host rock (i.e. the primary deposit where the sapphires formed) has not been identified. These sapphires are found in secondary, alluvial deposits.


Rough untreated sapphires from Jack Wilson's mine. L-R 10.21 ct and 6.54 ct.

After a long drive west, roads littered with dead kangaroos took us to Lightening Ridge, famous for its black opals. The town in the desert appeared empty. Tourists do not arrive until Easter. Only emus stay all year round. We camped in a site by the artesian baths, a wonderful way to relax and learn about the immense subterranean artesian system that probably played a role in the development of the opal fields. We visited an underground opal mine and were allowed to fossick for opals on the ‘mullock heaps’ of old spoil outside the mine. My husband found a small sample but I was not so lucky.

Next day we headed northwards. I was disappointed I could not buy any black opals in Lightning Ridge because the shops were shut, but a few kilometres before crossing into Queensland, a roadside sign led to the house, shop and workshop of Greg Armstrong. An opal miner, cutter and stone setter. Greg laid out his collection of white and black opal (3) and when we mentioned we were learning lapidary, he gave us a bag of ‘potch’ opal to practice cutting at home.

Boulder opals from Quilpie, mined and cut by Eddie Lunney.

Over the state boundary, we headed north for St. George, Roma, where the oil and gas industry’s mega coal bed methane (CBM) project produces gas from extensive Permian and Jurassic coal deposits to supply the energy needs of c. 90% of the homes in Queensland, and the location of the famous Carnarvon Gorge.

We drove inland to central Queensland to The Gemfields area, which includes the localities of Anakie, Rubyvale, Sapphire and Emerald, where green gemstones initially taken for emeralds were found in about 1880, when drilling for water, ahead of railway construction. Green and yellow sapphires and zircons have been mined in this area since the 1880s.

Read more: Field Trip: The 'Emerald Desert' in Western Australia

At the Sapphire Caravan Park we watched wallabies and lorikeets being fed. Taking Jack Wilson’s advice, we looked for Peter and Eileen Brown at the Rubyvale Gem Gallery, but as they were on holiday, the shop manager showed us Peter’s amazing fancy cuts on parti-colour sapphires. The shop is a gemmologist's paradise. Alicia Pray was cutting beautiful black star sapphire cabochons from the Desperado mine, and we bought a bag of ‘wash’ from the mine to fossick back home in Scotland.


Coloured sapphires collected over a period of 40 years in The Gemfields of Queensland by Peter Brown of the Rubyvale Gem Gallery.

Alan, a lively Stranraer émigré, took us round an underground sapphire mine in Rubyvale. Prospectors first dug one metre diameter vertical shafts through ‘shin cracker’ overburden (sandy gravels). The bottom layer of wash sits uncomfortably over eroded granite. When miners hit the granite at a depth of 15 m or so, they dug horizontal tunnels to follow the alluvial pay zone where sapphires, zircons, garnets and occasionally diamonds concentrate. Miners knew if they found a block of quartz in the wash, and sapphires were present, they were likely to aggregate upstream of such ‘Billy boulders’. This helped them to orientate their tunnels.

Geological section c.15m below the surface inside the Walk-in Miners Heritage Sapphire Mine at Rubyvale. The alluvial sapphires concentrate within narrow 'wash zones' (average 15-20 cm as marked by dotted lines) above the 'granite floor' and below several metres of sandy alluvial gravels. Elongated features are pickaxe marks.

From The Gemfields in Queensland, we drove westwards to Barcaldine ahead of cyclone Debbie's rainclouds. Here we decided to head south towards the Quilpie opal fields. As the land became more arid, the soil turned red, the gum trees thinned out and the grass grew sparse. Intrepid wildlife competed with massive ‘road trains’ for the driver’s attention on the empty roads between the gem locations. We passed trucks hauling three trailers, sometimes four.

Arriving in Quilpie, everywhere we went we were presented with useful information, friendly advice and ideas for things to see, and a chance to cool down from the 35 °C heat of early autumn in the outback. In Quilpie, they told us St. Finbarr’s Catholic Church was worth a look. Its altar, font and lectern have impressive panels of boulder opal donated in 1976 by local miner Des Burton, the father of the boulder opal industry. I was quite literally on my knees in adoration.

The only shop open in Quilpie sells everything. There I found the last copy of Greg Pardey’s Black Opal: A Comprehensive Guide to Cutting on its shelves and read it cover to cover before we got back to the UK. Walking back to the motorhome on our way out of town, we noticed that the Opal Hunter shop had opened too. Asking if I could buy some rough opal to cut back home, shop owner Eddy Lunney told me he would need to get to know me before knowing what he wanted to sell me. Induction into opal heaven started with a tour of the shop, the lapidary workshop and the yard with part of his huge stock of boulders from his opal mine. By teatime he had given me a masterclass in boulder opal cutting and polishing. I absolutely loved it! The dark blue and purple colours he brings out of the transparent opal (known as crystal) are gorgeous. It was really hard to leave Quilpie the next morning.

We noticed a change in the weather. The temperature had dropped to 20 °C as we drove to Yowah. In this famous opal location, we found Scott Shorten, shopkeeper, opal mine tour guide and librarian. After lunch, with his shopkeeper hat on, he showed us round the Yowah Opal Centre. Yowah opal is found inside nodules. Nine out of ten nodules are empty, so it is always exciting to crack open one, using a hammer or even better sawing through it, to see whether there is any opal inside. Scott sold us some good samples.

Before flying home, Matthew Morin FGA FCGmA senior sales consultant at Altmann + Cherny, a jewellers on Sydney’s Pitt Street, showed me how beautiful opals are used in modern jewellery (6). The shop also hosts The Olympic Australis, the largest and most valuable piece of opal ever found. It is a white opal from Coober Pedy, which weighs 17,000 ct, measuring 28 cm long by 11.5 cm high. For more information visit altmanncherny.com.au/famous

ACKNOWLEDGMENTS Carmen Garcia-Carballido would like to thank her husband, Peter Scott-Wilson, for organising the wonderful tour. Eddy and Lynda Lunney for their hospitality at Quilpie. Jack and Dallas Wilson, Robert Cook, Greg Armstrong, Scott Shorten, the staff at Rubyvale Gem Gallery and Matthew Morin for generously giving their time to discuss Australian gemstones.

Carmen meeting Matthew Morin at Sydney jewellers Altman + Cherny. Matthew is also the president of, and a gemmology tutor at the NSW division of the GAA (The Gemmological Association of Australia). Carmen is modelling a Koroit boulder opal pendant on white gold from the shop. Image by Peter Scott-Wilson.


Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Yowah boulder opals cut by Scott Shorten. Image by Carmen Garcia-Carballido.


The Fascinating History of Antique Turquoise Jewellery

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more


Birthstone Guide: Garnet For Those Born In January

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more


Getting Started with Quartz Inclusions

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more


Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more


Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more


Tanzanite: The Contemporary December Birthstone

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Birthstone Guide: Turquoise For Those Born In December

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more


Understanding the Cat's Eye Effect in Gemstones

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more


Jade and its Importance in China

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more


Highlights of Gem-A Conference 2019

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

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Additional Info

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The Lifecycle Of A Sapphire Rush

In the last 12 months, an exceptional sapphire rush in eastern Madagascar saw thousands of people searching for precious treasure in one of the poorest places on earth. Rosey Perkins GG, an independent gemmologist based in London, shares this report from two visits to the island nation.

A sapphire rush that started in September 2016 has produced world class sapphires close to the village of Bemainty, in the wet forest of eastern Madagascar has reached upwards of 45,000 people. The mine site was in an area called Corridor Ankeliheny-Zahamena (CAZ), which is designated for conservation and managed by Conservation International on behalf of the Government of Madagascar.

I gained access to the mines near the village of Bermainty in October 2016 and May 2017 and was able to capture the lifecycle of the mines that has become known as 'Tananarive Carrier' (18°00'00"N 48°67'83").

'Tananarive', which is the capital city of Madagascar, refers to its size and 'carriere' is Malagasy for 'mine'. It lies 135km NE of the capital and is accessed via the nearest town of Ambatondrazaka. From here a motorbike can be taken to the trailhead at Ansevabe. On 21 October 2016, the President of Madagascar had declared the mining activity illegal because it was inside CAZ. I arrived at the mine the following day. There was a sense of urgency and camaraderie as the miners anticipated imminent government intervention.


1: 100ct sapphire from Bemainty Mines.

The gendarme were present at the site to keep peace and monitor the mining activity. The mine was highly productive and in Ambatondrazaka, I was shown high-quality blue sapphire up to 50g, as well as desirably-coloured pink-orange sapphires, reportedly mined at Bermainty (1). However, in February, the Swiss Gemmological Institute (SSEF) issues a trade alert with the warning that sapphires from these mines were being misreported as Kashmiri (Krzemnicki, 2017). A preliminary study of sapphires from this deposit indicated that the origin of these sapphires would prove challenging for laboratories and that more in-depth analysis was needed (Pardieu, 2017). For this reason, Lotus Gemology needed samples and so it was thanks to them and Association Française Gemmologie that I returned on May 6, 2017.

At 5am, I started climbing the path towards the mine and 10 hours later, we reached the valley that had heaved tens of thousands of people in October. It was a wide valley carved with pits but in May 2017 only about 500 miners remained. The southern end had been almost abandoned and work was concentrated in the more productive central and northern areas, where old pits two to three metres deep were being reworked. Miners had left due to illness, lack of funding or to return to their previous jobs. In the nearby valleys that had been explored, many groups hadn't found a stone for months. (2&3).


2. Tananrive Carrier facing North in October 2016.


3: Tananrive Carrier in May 2017. Image by Rosey Perkins.

However, the mining area had been a valuable source of income during the months that the local population had waited for the rains, which came later than usual. They arrived as miners, porters or cooks to feed the growing community. Soon the exploration had moved into the adjoining valleys, which were named Milliard 1-4. In May, shreds of blue tarpaulin attached to the top of poles marked abandoned claims and only the skeletons of abandoned huts remained. Morale was low in the valleys, but a few months earlier they had been a source of hope (4).

At Tananarive Carrier families lived in two story huts and many had tents on the first floor with shops beneath. These were stocked with beer, local rum, vegetables and plenty of meat. There was a hut for gambling, a cinema with a projector and a board of power sockets offering electricity to charge mobile phones. There were two churches and a mosque but still no school and no sanitation. A doctor had visited for the month of November but the gendarme (law enforcement) said another was needed.


4: Abandoned section of Milliard 3. 'Milliard is French for 'Billion' and a billion ariary (the currency of Madagascar) worth of stones - approximately £300,000 - had been found in each.

Trading was open and the gendarme was relaxed. At the start of the rush there were many independent 'cooperatives' but in May 2017 most were from other mining areas in Madagascar, such as Diego Suarez, Sakahara and Fort Dauphin. Mining activity was mainly sponsored by businessmen from the major cities. They financed another 'sponsor' who stayed at the mine and hired men in groups, providing food and equipment in exchange for first refusal on the stones they found. At Tananarive Carrier I met an independent sponsor who employed 16 miners, eight security guards and a woman who cooked their meals. His miners formed two groups and shared the use of a motor pump. He supplied the equipment for digging, the fuel for their motor and food for the men. He said he spent approximately $35 per week on rice and meat for the miners and expected to sell a sapphire with 30%-40% profit.

Ambodipaiso and Sahambato were two mining communities that had sprung up by miners leaving Tananarive Carrier (5). They had stopped at a river, camped and dug a test pit or panned for gold and found sapphires. Movement between them was fluid and, as a large sapphire was found at one site, the response was an influx of people (6).


5: Ambodipaiso on May 6th 2017. Image courtesy of Zanaky Ny Lalana.

As miners continue to explore this gem-rich earth of eastern Madagascar, there may be a great many more rushes in the area (Pardieu 2017). While the Government of Madagascar has declared the mining activity illegal, they have not brought it to a halt. The media's coverage of this story has not portrayed the gem industry favourably and, as mining continues, pressure will be on the gem and jewellery industry to respond.

Impact assessments are being carried out by independent consultancies on behalf of businesses sourcing gemstones in Madagascar and the response is likely to be rehabilitation programmes in areas of land damaged by mining activity. A collective effort to support conservation would help sustain Madagascar's biodiversity and also demonstrate the gem industry's commitment to responsible sourcing.


6: Sapphires from Sahambato which resulted in an influx of people to the area.

Acknowledgements: Permission to enter CAZ was given by the Prefecture D'Ambatondrazaka, Direction Regionale de L'Environment De L'Ecologie et de Forets and the Bureau du Cadastre Minier de Madagascar. The gendarme permitted our team four days inside the areas and gave us two policemen as security guards. Thank you to Institute Gemmologie de Madagascar, Association Francaise de Gemmologie, Lotus Gemology and Vincent Pardieu for their time and support.

Gem-A members can log in to read the full article Gems&Jewellery Autumn 2017 / Volume 26 / No. 3

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image: The team walking from Ansevabe towards the miners. Two gendarmes (local police) joined them as a security measure. In October 2016, Rosey had counted 1,000 people travelling towards the mine. In May 2017 we passed less than 50. All images by Rosey Perkins, unless otherwise stated.


The Fascinating History of Antique Turquoise Jewellery

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more


Birthstone Guide: Garnet For Those Born In January

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more


Getting Started with Quartz Inclusions

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more


Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more


Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more


Tanzanite: The Contemporary December Birthstone

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Birthstone Guide: Turquoise For Those Born In December

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more


Understanding the Cat's Eye Effect in Gemstones

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more


Jade and its Importance in China

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more


Highlights of Gem-A Conference 2019

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more


 

Additional Info

Read more...

Inclusions Acting as Geological Fingerprints in Yellow Danburite from Vietnam

Guy Lalous ACAM EG summarises an article on inclusions in yellow danburite from Luc Yen, Vietnam, by Le Thi-Thu Huong, Kurt Krenn and Christoph Hauzenberger, originally published in Gem-A's The Journal of Gemmology. His report also examines optical characterisation of danburite and micro-Raman spectroscopy.

Danburite is a calcium borosilicate, CaB2Si2O8, belonging to the orthorhombic crystal system. It is genetically associated with rocks of magmatic (granite pegmatite), metasomatic (skarn) and sedimentary (evaporite) origins.


This 31.6g danburite specimen from the Bai Cat alluvial deposit in the Luc Yen mining area shows eye-visible hollow tubes and overlapping 'fingerprint' inclusions. Photo by L.T.-T. Huong.

What about metamorphism, marble and pegmatites?

When rocks change because of an increase in the pressure and/or temperature of their surroundings, it is called metamorphism. Marble is a metamorphic rock primarily composed of calcite, formed when limestone is subjected to heat and pressure. Pegmatites are igneous rocks. Igneous rocks are formed through the cooling and solidification of magmas. Pegmatites contain extremely large crystals and rare minerals. Most pegmatites have a composition with abundant quartz, mica and feldspar.

Černy's scheme (1991) is the most widely used classification of pegmatites. It combines depth of emplacement, metamorphic grade and minor element content. It is divided in 4 main categories. The abyssal (high grade, high to low pressure), Muscovite (high pressure, lower temperature), Rare-Element (low temperature and pressure), and Miarolitic (shallow level).

The Rare-Element Classes are subdivided based on composition into LCT type (Lithium, Cesium, and Tantalum enrichment) and NYF type (Niobium, Yttrium, and Fluorine enrichment). The Rare-Element Class if further subdivided into types and subtypes according to mineralogical/geochemical characteristics. Many pegmatites fall nicely into these categories but some of the Madagascan pegmatites are virtually unique and don't fit into these categories.

Luc Yen is a mountainous district located in the north of the Yen Bai providence in Vietnam. Ruby, sapphire and spinel have been recovered from primary and secondary deposits since 1987 in the Luc Yen area. The geology of Luc Yen is dominated by metamorphic rocks - mainly granulitic gneiss, mica schist, and marble - that are locally intruded by granite and pegmatitic dykes.

This paper is an updated description of the inclusions in danburite from Luc Yen, which were characterised by optical means and by micro-Raman spectroscopy. The original source rock type for this alluvial danburite is then proposed, according to information provided by the study of the inclusions.

Internal features in Vietnamese danburite consist of fingerprints, hollow tubes, and two-phase and multiphase fluid inclusions. The two-phase inclusions were typically composed of a liquid and a vapour bubble that showed various proportions, suggesting heterogeneous entrapment of the dominant fluid during crystal growth.

Most of the multiphase inclusions contained several crystals, a liquid phase and a vapour bubble. The crystals in the multiphase inclusions typically formed colourless euhedral pseudohexagonal plates; some of them displayed interference colours.


(a) Primary  multiphase inclusions occur singly or are arranged along trails, both parallel and perpendicular to the c-axis of the host danburite crystal. (b) The CO2 vapour bubbles in the two-phase inclusions vary in size, and in some cases only a thin layer of liquid is present along the inclusion walls. (c) Sassolite crystals in the multiphase inclusions appear as colourless, pseudohexagonal plates - sometimes displaying interference colours - with more-or-less perfect crystal faces. (d) Calcite crystals are occasionally associated with the sassolite plates in the multiphase inclusions. (e) This fluid inclusion contains multiple sassolite crystals accompanying two CO2 vapour bubbles and a liquid (H2O). Photomicrographs by K.Krenn.

What about Raman-spectroscopy?

In Raman spectroscopy the studied sample is illuminated with a monochromatic laser (single wavelength), the light is scattered by the sample. Light scattered from the sample is due to either elastic collisions of the light with the sample's molecules (Rayleigh scatter) or inelastic collisions (Raman scatter). Raman scattered light returns from the sample at different frequencies that are proportional to the vibrational frequencies of the bonds of the molecules in the sample. The Raman scattering from every molecule is different as the bonds for every molecule are different.

A Raman spectral 'fingerprint' can be generated. A database of reference spectra is necessary as the identification of a mineral by Raman spectroscopy is a comparative method. Raman spectrometry is useful to identify gems, inclusions and filling substances in gemstones.

What about sassolite?

Sassolite H3BO3, crystalline boric acid has been described for the first time as an inclusion in gas-liquid inclusions in minerals from the pegmatite veins Mika and Amazonitovaya in the Kukurt gemstone district in Central Pamir in 2000 (S.Z. Smirnov et al.). The crystals were rounded, tabular and less frequently idiomorphic with low refractive indices and high birefringence. The Raman spectrum of sassolite revealed an intense line near 880 cm-1 and a weaker one at 449 cm-1. The data obtained allowed reconstructing the conditions of formation of both granite pegmatites and hydrothermal systems where boron actively participated in mineral formation. Sassolite is a characteristic component of fluid inclusions in minerals from the majority of tourmaline-bearing and topaz-beryl miarolitic pegmatites.

Raman spectroscopy of the multiphase inclusions in the danburite samples revealed that most of the crystal inclusions were sassolite with occasional crystals of calcite. The sassolite showed two distinct bands at 500 and 880 cm-1 and two additional bands at 3165 and 3247 cm-1. The 500 and 880 cm-1 bands are assigned to vsB[3] -O species, where B[3] -O denotes three-coordinated boron. The calcite was characterised by two strong bands at 1088 and 283 cm-1 and a less-intense band at 714 cm-1.

The doublet at 270- 300 cm-1 in the Raman spectrum of the calcite might result from a combination of the intense calcite band at 283 cm-1 with the two nearby danburite bands (~281 and 296 cm-1). The liquid and vapour phases were identified by Raman spectroscopy as H2O and CO2, respectively. The spectrum of CO2 in the danburite fluid inclusions shows two diad peaks positioned at 1285.1 and 1388.3 cm-1. The diad split (known as the Fermi doublet) corresponds to low-density values, which points to a granitic pegmatite source rock for the danburite.


(a) Micro-Raman spectroscopy of the danburite fluid inclusions in the 150-1500 cm-1 range shows the presence of sassolite, calcite and CO2 vapour. The black trace shows only the bands of the host danburite. Labelled peaks are from the inclusion phases present. (b) Raman spectroscopy of the fluid inclusions in the 1500-3000 cm-1 range shows no bands from additional gas phases (e.g. N2 and/or CH4), but only luminescence signals of the host. (c) In the 3000-3800 cm-1 range, Raman spectroscopy of the fluid inclusions shows additional bands for sassolite (at 3165 and 3247 cm-1) and characteristic bands of water.

The various proportions of a carbonic vapour phase (CO2) compared to a liquid phase (H2O) indicate a heterogeneous entrapment of the fluid inclusions. This suggests that the associated sassolite and calcite precipitated as a result of decreasing temperature through hydration reactions with the host danburite. The presence of sassolite together with low-density H2O - CO2 fluid inclusions indicates the Luc Yen danburite originated from an organic pegmatite source rock.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Sassolite- and CO2-H2O-bearing Fluid Inclusions in Yellow Danburite from Luc Yeb, Vietnam’ by Le Thi-Thu Huong, Kurt Krenn and Christoph Hauzenberger 2017/Volume 35/ No. 6 pp. 544-549

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image: Hollow tubes in a 31.6g danburite specimen from the Bai Cat alluvial deposit in the Luc Yen mining area. Photomicrograph by L.T-T. Huong; field of view 2.5 cm.


The Fascinating History of Antique Turquoise Jewellery

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more


Birthstone Guide: Garnet For Those Born In January

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more


Getting Started with Quartz Inclusions

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more


Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more


Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more


Tanzanite: The Contemporary December Birthstone

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Birthstone Guide: Turquoise For Those Born In December

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more


Understanding the Cat's Eye Effect in Gemstones

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more


Jade and its Importance in China

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more


Highlights of Gem-A Conference 2019

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more


 

Additional Info

Read more...

Greenland Ruby: The Mighty Aappaluttoq Arises

With an opulent supply of rubies and pink sapphires, mining company Greenland Ruby is set to become an influential supplier of coloured gemstones. Here, International Women in Mining board member, Deborah Craig FGA DGA, shares her experiences in Greenland.

Greenlanders call the buried treasure of blood red rubies and vivid pink sapphires Aappaluttoq or "Big Red". Mining has now begun, positioning Greenland Ruby to become one of the market's most important suppliers of coloured gemstones. The rubies and sapphires will have an ethical pedigree that is increasingly important to buyers: responsibly-mined, with a transparent chain of custody and fully-disclosed treatments.

The new mine is also important to the people of Greenland, who voted for self-rule in 2008 with increased independence from Denmark. This means taking control of the development of their mineral resources and diversifying the economy from fishing and tourism, while creating self-sustaining tax revenues. Aappaluttoq is one of the first new industrial mines to come on-stream since this change went into effect.

Aappaluttoq is nestled between sea and glacier, 150 km south of the capital Nuuk, and east of the fishing village of Qeqertarsuatsiaat. The hilly, barren land is impassable, accessed only by small boat or helicopter (1). Geologists discovered significant ruby mineralisation in 2005; years of systematic exploration revealed the Fiskenaesset Anorthosite Complex. The metamorphic rocks that host the mineralisation are thought to be 2.9 billion years old, making Aappaluttoq one of the oldest coloured gemstone deposits worldwide.


1. The author and Jens Frederiksen, VP Security & Sales, Greenland Ruby. Helicopters are needed to reach the remote mine site.

A positive prefeasibility study was completed in 2011, after sufficient drilling and resource modelling. The ore is estimated to contain 10% corundum, of which 5% is gem quality, 20% near-gem quality (i.e. with inclusions), and 75% is commercial grade. The mine's profitability will depend on maintaining these robust grades, as well as efficiently extracting the gemstones from the ore.

Larger stones are found in the deposit, but their recovery is variable and difficult to predict. Therefore, only melee-sized rough material (<4mm) was included in the study and will underpin the steady sale of gemstones to the market. In this way, an industrial mine can provide a reliable supply of stones to jewellery manufacturers, something small alluvial operators cannot do.

Construction began in 2015 at a capital cost of US$25 million. Last fall, LNS Norway, parent company of Greenland Ruby, acquired the mine when previous owner True North Gems struggled to provide sufficient funding. LNS Norway has developed other projects in remote Polar Regions, including Antarctica and Svalbard. The mine is currently expected to operate for 9 years and produce 87 million carats of rough gemstones. Greenland Ruby is mapping and sampling its nearby Siggartartulik and Kigutilik projects, hoping to expand the mine's resource base.

The mine site will operate year-round and is staffed by Greenlanders flown to the camp for 2-3 week shifts. When possible, mine supplies are sourced locally, including fresh catches from local fisherman and hunters.

Aappaluttoq is a primary, hard rock deposit, containing two ore types: phlogopite hosts the higher chromium ruby, and leucogabbro hosts the pink sapphire (2). The ore is excavated from the open pit, mixed with lake water, and sent via conveyor belt on its circuitous route through the processing plant (3).


2. Aappaluttoq ruby in host rock.

A primary crusher reduces the size of the ore to below +60mm; a cone crusher reduces it further to below +20mm. After being washed, the crushed ore is mixed with a ferro-silicon solution (SG 2.7) in the dense media separation circuit and spun in a DMS cyclone. The heavy corundum sinks, and the lighter, floating waste material is diverted to tailings.

The corundum is separated into three size categories, before passing through a dry magnetic separator and an optical sorter. The optical sorter uses white light, a series of cameras, and a computer to identify red and pink crystals, triggering a pulse of pressurised air that separates the coloured material from the feed. The rough ruby and pink sapphire is transported from the processing plant to Nuuk, where any residual host rock is removed with hydrofluoric acid.


3. Aappaluttoq ore processing facility.

Greenland Ruby is currently calibrating its recovery process to reduce the amount of waste rock that makes its way through the system. This includes adjusting the conveyor belt speed so the optical sorter can work more effectively, and tweaking the hydrofluoric acid concentration and soak times.

The cleaned gemstones are sorted in Nuuk (4), against a customised master set of stones. First, the stones are divided into gem and near-gem qualities. Each of these qualities is then divided into four colour categories, ranging from deep red to intense pink to light lilac pink (5,6 & 7).


4. Holly Noahsen of Greenland Ruby sorts gemstones at the Nuuk office.

As noted by Christopher P. Smith, Andrew J. Fagan and Bryan Clark Craig in their article 'Ruby and Pink Sapphire from Aappaluttoq, Greenland' (The Journal of Gemmology, Volume 35/ No.4, 2016, pp.294-306), the stones have metamorphic-metasomatic type rubies and sapphires from other world deposits, including Montepuez.

They exhibit moderate to strong dichroism, have no visible colour-zoning, are are relatively high in chromium and iron and low in titanium, vanadium and gallium. Inclusions include clouds of minute rutile particles and some fine rutile needles, as well as arrowhead-shaped platelets.


Top left (5). Aappaluttoq ruby in matrix. Top right (6). Ruby crystal with triangular growth marks. Bottom (7). The sorters separate the stones by colour and clarity using a customised master set.

As Aappaluttoq is a primary deposit, the gemstones have been subjected to intense pressure and are most likely fractured. Removing the stones from their host rock is also difficult. This means that the majority of stones will need to be treated to improve their transparency, a process that also reduces their purple undertone. Treatments will be fully disclosed and the chain of custody will be carefully tracked. At present, Greenland Ruby will sell the treated rough material; the feasibility of bringing lapidary in-house is being examined.

Greenland Ruby has begun a soft launch of their rough rubies and sapphires. The company believes their strength lies in their ability to provide a steady supply of quality gemstones to jewellery manufacturers. Greenland Ruby is also considering strategic partnerships with select jewellery houses, to collaborate on marketing campaigns that will highlight the extraordinary provenance of Greenland rubies.

And the Greenland government and Greenland Ruby have the opportunity to develop an origin certification scheme, like the one that made Canadian diamonds a success story in a market increasingly looking for ethical sourcing alternatives.

Closer Insight

All that is red is not ruby on Greenland (8) - tugtupite, Greenlandic for "reindeer blood", is a silicate closely related to sodalite. Tugtupite is a much sought-after opaque to translucent, becoming redder in sunlight. Nuummite, meaning "from Nuuk", is a black opaque gemstone that exhibits iridescent flashes of colour due to its lamellar, fibrous structure (9).

8. Tugtupite in matrix: the gemstones becomes redder in sunlight.

Greenlandite (10) combines quartz and fuchsite to produce an opaque green stone that may be streaked with black schlieren or flecked with pyrite. Small scale miners extracting these stones have been supported by the Ministry of Mineral Resources with workshops on mining best practices, gemstone pricing and lapidary.


Left (9). Nuummite, only found near Nuuk. Right (10). Greenlandite with a schlieren vein.

The Ministry maintains an ongoing gemstone mapping project, compiling data from historical reports and noting when geologists and small-scale miners make interesting discoveries in the field.

Deborah Craig FGA DGA, would like to thank Greenland Ruby for sponsoring her field visit to Greenland.

All photos ©Deborah Craig, unless otherwise stated.

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image: Iceberg in coastal waters. Image ©Deborah Craig


The Fascinating History of Antique Turquoise Jewellery

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more


Birthstone Guide: Garnet For Those Born In January

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more


Getting Started with Quartz Inclusions

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more


Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more


Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more


Tanzanite: The Contemporary December Birthstone

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Birthstone Guide: Turquoise For Those Born In December

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more


Understanding the Cat's Eye Effect in Gemstones

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more


Jade and its Importance in China

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more


Highlights of Gem-A Conference 2019

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more


 

Additional Info

Read more...

Gold Fever in Arizona: Searching for Gold in the United States

With its legends of gold seekers and treasure hunters, Arizona is still drawing the gaze of gemmologists and history enthusiasts to this day. Gem sculptor Helen Serras-Herman FGA takes us on a journey to this 'gold fever' state.

Living in a state where gold in abundance had been discovered in the nineteenth and early twentieth centuries, it was only inevitable that I would, at some point, find myself amidst gold fever.

Some incredible specimens of gold in quartz, found in central and southern Arizona, are part of splendid collections at the Arizona-Sonora Desert Museum as well as the University of Arizona (UA) Mineral Museum in Tucson.

A short time ago I finished carving two beautiful specimens of gold in quartz from an undisclosed location in southern Arizona, a commission work for the 'Arizona Lapidary & Gem Rough' store in Tucson. Today's gold miners are as secretive about locations as were the old timers.


Left: The stunning gold specimen from the Huachuca Mountains in Cochise County is part of the splendid mineral collection at the Arizona-Sonora Desert Museum in Tucson. Middle: This beautifully formed gold specimen from the Vulture Mine resides in the Arizona-Sonara Desert Museum's mineral collection in Tucson. Right: This is one of two beautiful specimens of gold in quartz from an undisclosed location in southern Arizona that I just finished carving.

My husband and I recently visited the Superstition Mountains, the centre of many gold legends and treasure hunts. We brought back some great specimens of gold in quartz from the famous Black Queen Mine in Goldfield.

But how did Arizona become a 'gold fever' state? I looked to prominent Arizona historian Jim Turner, a retired professor, author, and friend for some historic perspective: "In the 1730s, Spanish prospectors worked deposits twenty miles north of the US-Mexico border in an area later called Oro Blanco (white gold) because silver in the ore gave it a whitish colour." Later, when miners (the '49ers as they are known) started coming back from California's gold rush in 1849, they came through Arizona and found placer gold and gold in quartz deposits. Placer gold, found in stream bed deposits, originates from ancient larger ore deposits, from which small gold flakes detach and roll downstream.


Two great specimens of gold in quartz from the Black Queen Mine in Goldfield mined several years ago.

The Superstition Mountains and Their Legends

The Superstition Mountains are located less than an hour's drive east of Phoenix, just past Apache Junction. It is an area of 160,000 acres of dangerous land filled with saguaros, gold legends and Apache curses, conquistador and Mexican miners' stories, Jesuits' hidden gold treasure legends, as well as over 250 mysterious deaths. Gold seekers and treasure hunters have been searching in vain for the mine that bore the legend of the Superstition Mountains, the Lost Dutchman Mine, named after Jacob Waltz, a German prospector known as the 'Dutchman'. It is believed that he found the richest gold mine in the world, possibly an old Spanish mine, but took the secret to his grave in 1891, leaving behind only some riddle clues.

The legend of the Lost Dutchman Mine still reels in treasure hunters, who follow those clues on old paper or stone maps that take them deep into the Superstition Wilderness, an areas of 242 square miles that are filled with steep canyons, rocky outcroppings, cacti and thick brush.

Among the many that have lost their lives searching there, are three treasure hunters from Salt Lake City, Utah, lost forever as recent as July of 2010. The dangers from the Apaches, who killed many in the region protecting their sacred land and igniting the legendary Apache curse, are now long over. However, the danger from the summer temperatures that soar well above 110 degrees, are real, and make it deadly to unprepared hikers.

Mineral prospecting has been banned since 1983 when the area became a national wilderness, yet every year many travellers hope that they will stumble across the fabled gold mine.


Left: The Superstition Mountain & Lost Dutchman Museum treasure maps. Right: Dutchman matchbox SM Museum. Rich gold in quartz ore, supposedly from the Lost Dutchman Mine.

Lost Dutchman Museum

For a safe way to learn about gold in Arizona, its mining history and legends, head to the Superstition Mountain & Lost Dutchman Museum. With a variety of exhibits that allow the visitor to see what the Old West was really like, the museum provides a wealth of information about the old gold mines of the area. With stunning displays of treasure maps and over 40 books about the legend of the lost gold, many of them out-of-print, you truly understand the power of the legends and the quest for gold. After looking at the book display, one is very thankful that he museum offers and extensive bookshop!

The Superstition Mountain

The Superstition Mountain & Lost Dutchman Museum is located on Hwy 88, the historic Apache Trail, now designated as Arizona's first historic road. The trail covers 47 miles from Apache Junction to Roosevelt Lake. The drive, at times very rough with steep grades, offers some fantastic views of the backside of the Superstition Mountains, as well as of the three lakes that dam the Salt River: Canyon Lake, Apache Lake and Roosevelt Lake.

Nobody else can describe the Apache Trail better than president Theodore Roosevelt, on his way in 1911 to the Roosevelt Dam dedication ceremony: "The Apache Trail combines the grandeur of the Alps, the glory of the Rockies, the magnificence of the Grand Canyon and then adds as indefinable something that none of the others have, to me, it is most awe-inspiring and most sublimely beautiful".

Goldfield Ghost Town and Mine

Following the Apache Trail north for only a short drive, you will reach Goldfield Ghost Town, which lies in the shadow of the legendary Superstition Mountains. This is a true 1890's boomtown that had 50 working mines in the district after rich high grade ore was found in the area in 1892.

The abandoned town was revived in 1988, and today you can ride a narrow gauge railroad that circles the town for a mile and a half, offering a narrated scenic ride of the historic buildings and the famous Black Queen, Bulldog and Mammoth Mines.


Guided tours of the Goldfield Mine take you underground to a reconstructed mine very close to the original, now flooded mine.

Exploring Goldfield History

At the Goldfield Historic Museum, in the heart of the ghost town, you can learn more about the first very rich gold strike in 1892 and the 4,000 miners that lived there for five rich years. There are 13 treasure maps on display, from the so-called old Spanish maps, to more recent ones. A wonderful little museum with very friendly staff eager to share their knowledge!

Guided tours of the Goldfield Mine take you underground to a reconstructed mine very close to the original, now flooded, mine. It is always worth listening to the well-versed guides on the history of the local mine, discover the gold mining equipment that was moved there from the original nearby mines, and learn more about the mining procedures.

The Vulture Gold Mine

The Dutchman, Jacob Waltz, also prospected in the Vulture Mine, and was employed there as a consultant. The mine is located northwest from Phoenix near the old historic town of Wickenburg, famous today for its Western flair. There, in 1863 Austrian immigrant Henry Wickenburg, discovered gold. Legend has it that he was trying to retrieve a vulture that he had shot, when he found the quartz outcropping. Although Wickenburg sold the mine after a few years, it became one of the most productive gold mines in the history of Arizona, producing gold worth more than 200 million dollars. The gold is embedded in the quartz ore, and requires hard rock mining. President Franklin Roosevelt closed the mine in 1942, during World War II. The miners left, believing they would return in 6 months, but the mine never re-opened.

The Vulture mine used to be open daily for self-guided tours when we last visited in 2011, but now it is accessible only via a two hour guided walking mine tour on Saturday morning 8:30-10:30am. It is a great place to visit and walk the trails that take you by the 'Glory Hole', the Blacksmith's Shop and the Main Shaft, the Assay Office, and the 80-Stamp Mill. At the Power Plant, which served as the Machine shop, time almost stood still. All the equipment is still there, just a bit dusty and rusty, waiting for miners. This is a rarely seen sight, eerie and awe-inspiring. All the tools are left in place, as if the workers are just out for lunch.


Goldfield as it is today.

Prospecting for Gold Today in Arizona

According to stats from Gold Maps OnlineTM their maps show currently 46,199 active gold claims and 364,629 abandoned claims in the state of Arizona on public lands.

A great resource for information about gold in Arizona is the 'Gold Prospecting' page of the Arizona Geological Survey's (AZGS) website.


Gold in quartz from the Black Queen Mine. This site was one of three major mines; along with the Bulldog and Mammoth Mine that made Goldfield famous in the 1890s.

Several associations in Arizona promote recreational gold planning and mining. Members of the Arizona Association of Gold Prospectors (AAGP) Phoenix Chapter usually go prospecting within one or two hours' drive from Phoenix, Mesa or Tucson. The Gold Prospectors Association of America (GPAA) is a national organization. With five chapters in Arizona, there are plenty of locations and options to follow your gold fever.

For a two hour gold panning adventure join Apache Trail Tours, an award-winning our company based in Goldfield Ghost Town offering guided tours from one to eight hours.

If by now, you are sweltering from gold fever, besides going prospecting with any of the local gold clubs or purchasing gold specimens, you can buy your own gold mine in Arizona. My husband is already checking his wallet!

Next time you visit Arizona, please take a trip to these wonderful historic sites, museums and mines; they will enhance your knowledge about the difficulties of gold hard rock mining, the thrill of placer gold panning, as well as the successes and failures of gold-seeking. You may be inspired to go gold prospecting, or simply enjoy all the legends disseminated for over a century.

Sources

For currently available claims, please visit: goldmapsonline.com/arizona-gold-map.html, azgs.az.gov/minerals_gold.shtml, arizonagoldprospectors.org, goldprospectors.org, apachetrailtours.com, goldrushexpeditions.com/state/arizona/.

All images courtesy of Helen Serras-Herman.

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Goldfield Ghost is an abandoned town, revived in 1988, filled with museums, shops, and an underground mine, all in authentic-looking buildings. Image ©Helen Serras-Herman.


The Fascinating History of Antique Turquoise Jewellery

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more


Birthstone Guide: Garnet For Those Born In January

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more


Getting Started with Quartz Inclusions

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more


Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more


Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more


Tanzanite: The Contemporary December Birthstone

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Birthstone Guide: Turquoise For Those Born In December

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more


Understanding the Cat's Eye Effect in Gemstones

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more


Jade and its Importance in China

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more


Highlights of Gem-A Conference 2019

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more


Additional Info

Read more...

The Source of Garnets Found at The Arikamedu Archaeological Site in South India

Guy Lalous ends the year with his final Journal Digest of 2017 by exploring the chemical and mineralogical characterization of garnets found at the Arikamedu archaeological site in South India and their linkage to the rough material sourced from the Garibpet Deposit, roughly located 640 km away in Telangana State, east of the city of Hyderabad, India.

What about silicates and nesosilicates?

The vast majority of the minerals that make up the rocks of Earth's crust are silicate minerals. These include minerals such as quartz, feldspar, mica, amphibole, pyroxene, olivine, and garnets. The building block of all of these minerals is the silica tetrahedron, a combination of four oxygen atoms and one silicon atom. Garnets are nesosilicates. This subclass includes all silicates where the (SiO4) tetrahedrons are unbounded to other tetrahedrons.

What about garnets?

Garnets are a set of closely related minerals that form a group, resulting in gemstones in almost every colour. All garnets have essentially the same crystal structure, but they vary in chemical composition and properties. Many garnets are chemical mixtures of two or more garnet species, they are found throughout the world in metamorphic, igneous and sedimentary rocks. They have been grouped according to their composition in two groups. The ones that contain A1 in the B position in the formula are widely called pyralspites and the ones with Ca in the A position are ugrandites. These names are derived from the first letters of the single minerals in these groups; pyrope, almandine and spessartine make up the pyralspite and uvarovite, grossular and andradite are the members of the ugrandite group.

Garnets are isotropic and figuring out how each one of them fits into the six main mineral species and their mixtures can be a serious challenge. The gemmologist will need an accurate refractive index, specific gravity and UV-VIS spectrum to come to the right conclusion.


Table of identification of the main garnet species.

What about Arikamedu?

Arikamedu has initially been portrayed as a Roman settlement. Modern theories describe Arikamedu as an important Indian trading centre and harbour, connecting the east coast of India with the western world from the 1st century BC to the 7th century AD. Arikamedu served as one of the main bead-producing localities in India. The unearthing of several thousand stone and glass beads during the archaeological excavations attests to this fact. The glass is rich in potassium oxide K2O (Harder 1993). Some of the beads collected are cobalt glass with following gemmological properties: R.I.=1.52 spot, gas bubbles, swirl marks and chalky fluorescence (Jayshree Panjikar, Pangem Testing Laboratory, Pune, India). Garnets were the second-most prevalent among the stone beads after the quartz variety. Bead production remained on-going in the region for centuries and was only abandoned in the early 17th century.

The current study presents for the first time a thorough chemical and mineralogical characterization of garnets found at the Arikamedu archaeological site in southern India, using high-quality major- and trace-element data in conjunction with detailed inclusion studies. The authors then demonstrate a remarkable correlation with recently mined garnets from Garibpet in Telangana State, India - approximately 640km away of 760km distant by road - as the source of origin.

The Kothagudem-Garibpet area is located in the Vinjamuru domain of the Khammam schist belt and consists of Paleoproterozoic moderate-grade (and partly migmatitized) metasediments and metavolcanics with minor mafic and granitic intrusives. The conspicuous Garibpet Hill is formed of garnet-kyanite-muscovite schist and is surrounded by biotite schist and gneiss.


These faceted garnet beads were collected by local farmers from the Arikamedu site. The samples constitute some of those studied for this report and measure ~4.55-5.5 mm in diameter. Photo by K. Schmetzer.

What about Electron Microprobe Analysis?

During electron microprobe analysis, a sample is bombarded with a beam of electrons. The interaction of the electron beam with the sample material results in formation of X-rays, which can be analysed by the microprobe. The wavelengths and energies of these X-rays provide information about the chemical elements present in the sample (qualitative analysis). When compared with reference materials, the measured x-ray intensities can be used to determine element concentrations (quantitative analysis).

What about a Ternary Diagram?

A ternary diagram is a triangle, with each of the three axes representing a composition, such as the one in this study: pyrope, almandine and spessartine + grossular. The proportions of the three compositions sum to 100%. The plot graphically depicts the ratios of the three variables in as positions in an equilateral triangle. It is used in physical chemistry, petrology, mineral and other physical sciences to show the compositions of systems composed of three species.

The great majority of analysed samples from Arikamedu (beads and fragments) and the rough stones from Garibpet proved to be garnets with a high almadine content. The compositional fields were in close proximity and overlapped to a large extent. Microprobe data revealed almandine in the range of 77-84 mol% with minor components of pyrope, spessartine and grossular. A ternary plot of the molecular percentages of the garnet end members pyrope and almandine and the sum of spessartine + grossular showed that the studied garnets plotted within a relatively small compositional range. This outcome was even clearer when only a small portion of the full ternary diagram was drawn with an extended scale.

(a). This ternary diagram shows the chemical composition of garnets from Arikamedy and Garibpet calculated for the molecular end-members pyrope, almandine and spessartine + gossular. The compositions plot in a concentrated area, except for two anomalous Arikamedu samples (blue and purple arrows) that fall outside the main compositional field, which are inferred to be from different sources. (b). An enlarged detail of the main compositional field for the Arikamedu and Garibpet garnets corresponds to the area defined by the grey triangle in the inset. Note the extensive overlap in the composition of garnets from Arikamedu and Garibpet.

The compositional ranges for the two localities were:

  • Arikamedu: 77.4-83.5% almandine, 10.2-14.2% pyrope, 0.9-5.3% spessartine, 0.9-2.5% grossular
  • Garibpet: 79.2-84.0% almandine, 9.6-12.0% pyrope, 1.1-5.9% spessartine, 0.6-2.1% grossular

How does LA-ICP-MS work?

The LA-ICP-MS analysis process can be thought of in two main parts: material sampling i.e. Laser Ablation (LA) and chemical analysis i.e. Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A tiny, nearly invisible ablation put is caused by the laser, into the girdle of the gemstone. There will be minimal damage as the laser vaporises only a microscopic amount of the sample for analysis. It nebulizes the material and the aerosol produced is transferred in a gas stream to an ICP-MS for elemental and/or isotopic analysis. An ICP-MS combines a high-temperature Inductively Coupled Plasma (ICP) with a Mass Spectrometer (MS). The ICP is an ionisation source where the energy is supplied by electric currents, which ionises the atoms. These ions are then separated based on their mass-to-charge ration (m/Q) and detected by the MS.

What is LA-ICP-MS used for?

LA-ICP-MS is recognised as one of the most important spectrometric techniques and has been used in gemmology for quantitative chemical analysis. It provides data that can be used to create chemical fingerprint diagrams for geographical origin determination.

The compositional averages and the ranges demonstrated by LA-ICP-MS analyses were nearly identical for the Arikamedu and Garibpet garnets. A similar relationship was noted for lanthanide rare-earth elements. Several samples from Arikamedu and Garibpet also showed chemical zoning for some trace elements, such as Y, P and Zn. Considering in detail both trace and other elements, chemical zoning between core and rim was strong for Mn and significant for Ca, largely consistent with the results of microprobe analyses.

How can we classify solid inclusions?

Solid inclusions are divided into three categories, by time of entrapment: those formed before the host crystal, called protogenetic; solids which arise from the solution from which both they and the host originated, called syngenetic and those formed after the host crystal has finished its growth, epigenetic.

The proto - to syngenetic inclusions in the cores comprised, with decreasing abundance: apatite, quartz, ilmenite, rutile, monazite, zircon, graphite and fluid inclusions. At the core-rim boundary, a very characteristic layer of fibrous sillimanite bundles was observed. Isolated zircon, monazite and quartz crystals were also found occasionally in the rims. The garnets were often cut by brownish-yellowish fractures coated by various generations of goethite or other iron oxides-hydroxides.


Coarse acicular sillimanite needles were observed in a small number of the garnets from Arikamedu. Photomicrograph by H.A.Gilg.

The small differences observed in the average chemical compositions between the Arikamedu and Garibpet material can probably be explained by the fact that the Garibpet samples were collected from one secondary source within a large garnet-bearing area and, therefore, are not entirely representative of the Garibpet rough material used for bead production at Arikamedu.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled 'The Linkage Between Garnets Found in India at the Arikamedu Archaeological Site and Their Source at the Garibpet Deposit’ by Karl Schmetzer, H. Albert Gilg, Ulrich Schüssler, Jayshree Panjikar, Thomas Calligaro and Patrick Périn 2017/Volume 35/ No. 7 pp. 598-627

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Cover image: Faceted garnet bicones from Arikamedu were cut in half and polished for microprobe analysis. Two drill holes meet approximately in the centre of each sample. Photo by H.A.Gilg.


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