The beautiful and enchanting gemstone turquoise is one of three birthstones for December, enriched with cultural significance and ancient medieval lore. Join us as we explore the blue hues of this gemstone in our final birthstone round-up of 2017.
One of the first gemstones to be mined and used in jewellery, turquoise is one of three birthstones for the month of December. Admired since ancient times, this gemstone is known for its beautifully unique colour, ranging from powdery blue to an unrivalled 'robin's egg' blue. Its colour and historic significance have resulted in turquoise becoming a favourite of many.
Displaying the different properties of turquoise: cut, clarity, colour and carat weight. Photos ©Gem-A
Gem turquoise is a polycrystalline copper material typically occurring in thin seams or small nodules. Turquoise is found in dry, barren, arid regions where copper, leached from rocks by rainwater, reacts with aluminium and phosphorus. The result of this reaction is a porous, semi-translucent to opaque compound of hydrous copper aluminium phosphate with some evidence of iron. Copper produces the blue hues whilst chrome and iron add tonal variations of green.
Quite often, small patches or veins of brown or black host rock, known as matrix can be seen in the stone. The presence of these 'spider-web' patterns can often lower the value of the stone. However, some buyers actively seek stones with a presence of its matrix as they can be more unusual and attractive.
In terms of market-value, turquoise stones completely free from traces of matrix command a higher value, whilst those with evident spider-web patterns classified as desirable fetch second-place value in the trade.
Turquoise simulant; paste. Photo courtesy of Pat Daly.
The earliest evidence we have of this gemstone dates back to 3000 BCE, under the reign of King Tut, within the oldest turquoise mines located in the Sinai Peninsula of Egypt. Extraordinary pieces with elaborate displays of turquoise were found on the gold jewellery of many Egyptians, with the most extravagant display found set on the iconic burial mask of King Tut himself.
Ancient Persians believed that turquoise guaranteed protection and adorned many of their palace domes with the sky blue gemstone which they considered to represent heaven. Additionally, ancient Persians often engraved Arabic script into turquoise which would then be used to intricately decorate their daggers and horses' bridles. The highly prized 'robin's egg' blue - also known as 'Persian turquoise' - was venerated by the people of Persia (now known as Iran) as well as Siberia, Tibet, Turkey and Afghanistan. It was the Turkish traders who later introduced this 'Persian blue' stone to Europe in the 13th century through the Silk Road.
Map of localities where turquoise is found throughout the world.
The texture of turquoise is a direct result of its composition and structure. As an aggregate, polished turquoise with a smooth waxy lustre has a tightly-packed crystal structure, low porosity and a fine texture. Turquoise gems displaying a dull lustre when polished have a coarser texture and increased porosity due to a less-dense internal crystal structure. This range in texture and porosity not only directly affects the overall appearance and lustre of this gemstone but also influences its durability.
Typically, turquoise is a fairly soft stone which made it a popular choice for talisman carving across ancient history. Throughout America, many carvers fashioned turquoise into amulets of Native American significance such as birds and animals.
Collection of turquoise stones. Photo courtesy of Pat Daly.
With a hardness of 51/2 - 6 on the Mohs scale and a fairly good toughness, turquoise is a suitable material in the use of jewellery. That being said, the toughness of turquoise is significantly less in stones of a coarser texture. This December birthstone is sensitive to direct sunlight and natural solvents such as perfume, oils and makeup products. Due to its porosity, turquoise that is polished and faceted for commercial jewellery is often treated with paraffin compounds in order to increase its durability by oiling or waxing the surface of the stone.
Ancient History and Lore
Turquoise has been continuously admired as a stone of considerable meaning and sentiment across many cultures for thousands of years. As one of the world's most ancient gemstones, this highly esteemed stone has been used to decorate many artefacts from jewellery to ceremonial masks.
Turquoise simulant; Dye-treated magnesite. Photo courtesy of Pat Daly.
Archaeological evidence shows that not only was this gemstone used to embellish ancient Egyptian ornaments but was also a primary carving material for Chinese artisans. For many Native Americans, turquoise held great ceremonial value in being an instrument of exchange between tribes. As the national stone of Tibet, turquoise is enriched with ancient lore of being a symbol of good health, fortune and success. Often referred to as a token of protection, turquoise was commonly worn to ward off the presence of evil spirits, granting its wearer a sense of power.
All photos courtesy of Pat Daly at Gem-A.
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Cover image Surface patterns and textures of different cabochons of turquoise. Images courtesy of Pat Daly ©Gem-A.
Featured in the Spring 2018 issue of Gems&Jewellery, Rui Galopim de Carvalho FGA DGA explores how ‘alternative facts’ have resulted in an informal nomenclature that permeates the world of gemmology. Here, he offers some examples of these long-standing quirks in terminology.
From the the Spring 2018 issue of Gems&Jewellery, here Harold Killingback FGA explores chatoyancy in sillimanite cabochons, an optical phenomenon where a band of light, known as a 'cat's eye', appears to hover above the surface of a stone, resulting in a striking lustre and colour.
Every year Gem-A gives its members and students the chance to show off their skills with the camera through the Gemstone Photographer of the Year competition. Have you got what it takes to be Gem-A's best photographer of 2018? Entries are open now and close on August 31, 2018.