Birthstone Guide: Ruby for Those Born in July

For those born in July, your birthstone is the resplendent ruby. Here, Gem-A tutor Lily Faber FGA DGA EG delves into the properties and folklore of this brilliant red gemstone. 

The ruby slippers, a ruby red apple, ruby red lips. For those interested in gems and jewellery, and even those who aren’t, rubies are synonymous with a rich, red colour.


"The Sunrise Ruby" 
Burmese ruby weighing 25.59 carats Sold for $30,335,698 ($1,185,451 per carat), at Sotheby’s Geneva, May 2015. ©Sotheby’s

What many don’t know is that the ruby is a member of the corundum gem species along with sapphires, the difference being colour and colouring elements. Rubies are specifically red, coloured by chromium, while sapphires have more flexibility with their colours (including blue and any other colour aside from red). The most valued red is called ‘pigeon’s blood’—a deep, rich red that is seen to be the purest iteration of the colour.

It is believed in some cultures that rubies bring prosperity and protection to those who wear them. Rubies are also the stone of passion, associated with love. It has even been said that rubies should be rubbed on one’s skin to promote or restore your youth.

Historically, all red gemstones were called a ruby until the late 18th century when gemmology developed as a science and people were able to distinguish between various species of red stones. In fact, some of the most famous rubies, including the Black Prince’s Ruby and the Timur Ruby in the Crown Jewels, are in fact red spinel.

Crystals and Inclusions

The most common crystal habit for a ruby is a flat, tabular hexagonal shape that can be either sharp or rounded on the edges. There may be raised, triangular growth marks on the top or bottom pinacoids of the crystal, as well as some lamellar twinning lines on the sides of the crystal. These are distinctive crystals and can be readily recognised. Twinning occurs when a crystal changes its direction of growth during formation either once or multiple times.


Ruby, crystal inclusion with twinning and twinning host. Photo by Pat Daly. 

Rubies can contain a large variety of inclusions. These can be crystals, feathers (partially-healed internal fractures), silk (long, thread-like rutile inclusions), evidence of the lamellar twinning in the form of twin planes, and hexagonal colour-zoning.  Silk, which forms in three directions at 120 degrees, can cause an optical effect known as asterism (a bright star that appears in the stone), which is highly valued in natural rubies. You can often tell if a ‘star-ruby’ is a natural one as opposed to a synthetic one because the star is not always centred, the arms of the star are slightly crooked or diffuse and the cabochon has a rounded or deep base to preserve yield, therefore raising the price of the stone.  

Pre-treated and treated ruby. Photo by Pat Daly.

Treatments

The most common treatment to corundum as a whole is heat treatment to enhance or remove colour. For rubies, brown and blue tones are often removed by this method. Additionally, it is important to watch out for rubies that have been fracture-filled with lead glass to improve colour and clarity. This treatment is becoming more and more prevalent, so caution is advised when buying rubies. The lead glass leaves tell-tale signs, however, so look for surface-reaching fractures, a difference in surface lustre between the glass and the ruby, and a blue flash within the ruby as well as bubbles, both of which are confined to the fractures inside of which the glass sits. It is not advisable to heat these rubies as the lead glass has a low melting point and will leak out of the stone.

Heat-Treated Crystal and Feather Inclusion. Photo by Pat Daly. 

Care and Caution

Rubies are comparatively hard at 9 on the Mohs scale of hardness, second only to Diamonds with a hardness of 10. They are excellent stones to set in jewellery due to their ability to resist scratches as well as any chemical attack. It is not advisable, however, to put them in an ultrasonic or steam cleaner, especially if stone is fractured or has been lead-glass filled.

Rubies are a historic gem, considered to be the gem of royalty. Whether you appreciate them for their colour, multitude of inclusions, or their stature within the gem community, they are a worthy addition to anyone’s jewellery box, especially if you were born in July.

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: Crystal and Feather Inclusion. Image by Pat Daly.


Journal Digest: Bumble Bee Stone from Indonesia

Journal Digest: Bumble Bee Stone from Indonesia

Guy Lalous ACAM EG delves into an article on Indonesian Bumble Bee Stone (BBS) from The Journal of Gemmology Volume 36, No.3, and presents his edited take on the most essential information, findings and lessons to be learnt. Continue reading here...

Read more


Field Trip: A Visit to Gem-A ATC Institut de Gemmologie de Madagascar

Field Trip: A Visit to Gem-A ATC Institut de Gemmologie de Madagascar

Gem-A tutor Barbara Kolator B.Sc. M.Sc. FGA DGA EG shares some highlights from her recent trip to the Institut de Gemmologie de Madagascar in Antananarivo, which is a proud Gem-A Accredited Teaching Centre (ATC). 

Read more


Natural Pearls: Marie Antoinette's £27.8 million Precious Pendant

Natural Pearls: Marie Antoinette's £27.8 million Precious Pendant

Famous for her ostentatious sense of style, 18th century French Queen Marie Antoinette was back as the centre of attention at Sotheby's in November thanks to the record-breaking sale of her natural pearl and diamond pendant. Here, Beth West FGA DGA EG considers the history behind this fascinating piece. 

Read more


Birthstone Guide: Tanzanite for Those Born in December

Birthstone Guide: Tanzanite for Those Born in December

Looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers the December birthstone tanzanite and how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more


Retail Focus: Beyond the Green

Retail Focus: Beyond the Green

From the Summer 2018 issue of Gems&Jewellery, Gem-A Gemmology Tutor Beth West FGA DGA EG explores Colombian emeralds. 

Read more