Ruby is a variety of the mineral species corundum and has been a popular gemstone for centuries. It has picked up many legends along the way. People in India believed that rubies enabled their owners to live in peace with their enemies. In Burma (a ruby source since at least 600 AD — now called Myanmar), warriors wore rubies to make themselves invincible in battle.

Rubies were worn in medieval Europe to guarantee health, wealth, wisdom, and success in love. As the US birthstone for July, ruby still captivates the hearts and imaginations of gem professionals and consumers alike.

Large, fine-quality rubies are extremely rare and valuable. But strong worldwide production and an array of treatments have increased availability and put rubies within the reach of most customers.

Common cutting styles for ruby include mixed-cut ovals or antique cushions for transparent material, and cabochons or beads for translucent to opaque stones. Corundum has excellent toughness, and it's harder than any other natural gem except diamond. This makes it ideal for rings as well as many other types of jewelry.

The name ruby comes from the Latin word ruber, which means "red." The most expensive ruby colour is a deep, pure, vivid red. Stones a little pinkish, purplish, or orangey red are also considered rubies, but gem and jewellery professionals make careful distinctions between ruby and pink, purple, or orange sapphire. (Ruby and sapphire are both corundum varieties.)

Generally, the difference depends on a combination of hue, tone, and saturation, but market culture and geography also make a difference. Gems that would be considered pink or purple sapphire in the US may be classified and sold as rubies in some Asian countries.

Major Sources
Afghanistan, Kenya, Madagascar, Myanmar (Burma), Sri Lanka, Tanzania, Thailand, Vietnam.

Hardness & Toughness
Ruby has a hardness of 9 on the mohs scale, and usually has excellent toughness. Stones with certain treatments or large fractures or inclusions may be less durable.


Heat can cause a change in colour or clarity, it can also damage or destroy fracture- and cavity-fillings. Rubies are generally stable to light, but bright lights can cause oil to leak or dry out. Chemicals can harm fillings and remove oil; soldering flux containing boron and firecoat made with boric acid powder, will etch the surface of even untreated stones.

Improves colour and/or clarity appearance
Stability: Stable unless the stone is heated to very high temperatures
Prevalence: Very Common; experts estimate that up to 95% of stones undergo some sort of heat treatment
Detection: May be detectable by a trained gemologist of gemological laboratory.* Can be undetectable, but assumed because of prevalence

Surface diffusion (heating to very high temperature in the presence of a colouring agent)
Creates a very shallow layer of red colour in colourless or light coloured sapphire
Stability: Stable under normal conditions, but the colour layer can be damaged or destroyed if the stone is repolished or recut
Prevalence: Occasional. Diffusion-treated red corundum should not be called ruby
Detection: Detectable by a trained gemologist or gemological laboratory*

Fracture-filling with oil or epoxy resin
Improves clarity appearance by hiding fractures. Coloured oil or resin also improves colour appearance
Stability: Fair. Heat and chemicals can damage or destroy the filling. Oil will probably dry out or discolour in time
Prevalence: Occasional
Detection: Detectable by a trained gemologist or gemological laboratory*

Cavity-filling with epoxy resin or glass
Improves clarity appearance by hiding cavities; adds weight if the cavities are large
Stability: Fair. Heat and chemicals can damage or destroy the filling
Prevalence: Common
Detection: Detectable by a trained gemologist or gemological laboratory*

* If there is any doubt, send the gem to a gemological laboratory for verification.

Care and Cleaning
Rubies can be cleaned in warm, soapy water, but avoid strong detergents and vigorous scrubbing on oiled stones. Ultrasonic cleaning and steam cleaning are usually safe, but never for fracture- or cavity-filled stones.


Flame fusion
Floating zone

This article is reproduced by kind permission of GIA

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