Birthstone Guide: Ruby for Those Born in July

Ruby the red variety of corundum occurs as bright-red, red, purplish- or brownish-red, and deep pinkish-red hues, coloured by chromium. It is the birthstone for those born in July.

The toughness, stability and hardness of both natural and synthetic ruby, coupled with its red fluorescence means it is not just desirable in jewellery, but also used in watchmaking, lasers and medical instruments. Diamond is the only gemstone harder than ruby.

Cleavage None
Hardness 9
Stability Very Good
Toughness Excellent

The colouring element chromium in ruby, can cause fissures and cracks, so few crystals large enough to be classified as gem quality ruby are found naturally. This rarity, along with is desirable characteristics make ruby a precious and expensive purchase. 

Barrel shaped ruby crystal. Image courtesy of Pat Daly.
Barrel shaped ruby crystal. Image courtesy of Pat Daly.

Three important factors of quality affect the value of the gemstone: colour, clarity and quality of cut. The highest value stones have a good rich colour, are free from inclusions and have a bright, lively appearance. 

Commercial quantities of ruby are found in numerous locations including Myanmar, Pakistan, Afghanistan, Thailand, Sri Lanka, Tanzania and Vietnam. These locations have fairly distinctive inclusions to aid identification, but the inclusions are frequently seen in gemstones from other areas and may occur in stones from other localities such as Australia, Kenya, Namibia, Madagascar, India, USA, Russia, China and Nepal.

Crystal inclusions in ruby from Myanmar. Image courtesy of Pat Daly.
Crystal inclusions in ruby from Myanmar. Image courtesy of Pat Daly.
LocalityTypical Inclusion and Features
Myanmar (Mogok district) Commonly contain short, fine rutile needle inclusions known as silk. A variety of mineral inclusions are also seen. Inclusions may be well-formed, or corroded rounded crystals. Intersecting twining planes often seen.
Pakistan Similar to those from Myanmar in colour but clarity is often poor, generally stones are cut as cabochons.
Afghanistan Often contain blue patches, as well as calcite, mica and rutile inclusions. Usually found in small sizes.
Thailand Naturally darker, brownish-red in colour. Often have irregularly-shaped fluid inclusion with dark crystals at their centres. Heat treated stones may be similar in colour to stones from Myanmar. Weak fluorescence is seen due to iron content. Intersecting twining planes often seen.
Sri Lanka Stones contain long, coarse, rutile needles, biotite mica, pyrite, metamict zircon grains with tension hales, pronounced hexagonal colour zoning, elongate negative crystals or cavities containing fluid and/or crystals. Red and pink in colour.
Tanzania Stones found in Longido are often of fine colour, found in a bright green chrome zoisite rock. Due to clarity stones are cut as cabochons. In the Umba valley facetable material is found showing twinning planes and apatite crystals. Morogoro is where star material is found.
Vietnam Fine colour, good clarity, similar to Myanmar rubes. Most material contains blue patches, which can be removed or modified by heat treatment.
Dark crystal and feather inclusions in ruby from Thailand. Image courtesy of Pat Daly.
Dark crystal and feather inclusions in ruby from Thailand. Image courtesy of Pat Daly.

A sixteenth-century writer wrote of the July birthstone that it: "gave control of the passions, drove out evil thoughts, secured possessions to their rightful owner, reconciled quarrels, brought peace and concord and also preserved bodily strength and health." In the past many red stones with a good hardness and lustre, including ruby, spinel and garnet were referred to as ruby. As gemmological knowledge improves, the differences between these materials is more easily identified, although incorrect identification does still occur. Materials with a similar appearance today include red glass, red tourmaline, almandine pyrope garnet, red spinel, red garnet-topped doublet and corundum-corundum doublet. ■

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 ruby with rutile inclusions. Image courtesy of Pat Daly. 

How to Separate Natural from Synthetic Ametrine using Conventional Equipment

How to Separate Natural from Synthetic Ametrine using Conventional Equipment

Guy Lalous ACAM EG summarises the discovery of features that could be used to distinguish between natural and synthetic ametrine from The Journal of Gemmology; from the orientation of growth striations to the interference patterns caused by twinning.

Read more


Speaker in the Spotlight: Q&A with Evan Caplan

Speaker in the Spotlight: Q&A with Evan Caplan

One of the key speakers at this year's Gem-A Conference, Evan Caplan will discuss everything about the extraordinary gemstone, alexandrite including a little history, information on sources (old and new), colour change, cutting, along with some fun stories about his travels and experiences with alexandrite.

Read more


Magnificent 51ct Dynasty Diamond Unveiled by Russian Mining Giant

Magnificent 51ct Dynasty Diamond Unveiled by Russian Mining Giant

Russian diamond mining company, Alrosa, has unveiled the extraordinary centrepiece to its unique Dynasty collection of five diamonds, the Dynasty Diamond.

Read more


GIA Pioneer and Leading Librarian Dona Dirlam Retires after 38 Years

GIA Pioneer and Leading Librarian Dona Dirlam Retires after 38 Years

The Gemmological Institute of America (GIA) has announced that after 38 years Library and Information Centre Director, Dona Dirlam, has retired, leaving behind a legacy of excellence and a pioneering approach to digitisation of gemmological knowledge.

Read more


Complete Traceability and Ethical Sourcing

Complete Traceability and Ethical Sourcing

Columbia Gem House president, Eric Braunwart, explores the growing popularity of American gemstones and discusses the importance of traceability, ethical sourcing and the millennial consumer with Sarah Jordan.

Read more


Speaker in the Spotlight: Q&A with Samanta & Vladyslav Yavorskyy

Speaker in the Spotlight: Q&A with Samanta & Vladyslav Yavorskyy

A charismatic duo who have turned their lifelong devotion to natural beauty into not only a solid business but also an expression of art; meet the most intriguing team of two in the world of gems, Vladyslav and Samanta Yavorskyy.

Read more