Ruby
Ruby is from the Latin word for red and is found in various shades of purplish, pinkish, orangey and brownish-red as well as the rare pure red colour. The finest rubies are described as pigeon blood red, with good clarity and good fluorescence in sunlight and incandescent light. These are very rare and exceed the price of diamonds carat for carat. The most prized rubies came from deposits in the Magok area of Burma (now Myanmar) recently reported as mined-out. Rubies are mined in other areas of Myanmar and are still referred to as Burma ruby.
There are many famous rubies throughout the world, set in Crown Jewels and kept in private collections. With the event of gemmological testing and analysis, some gemstones previously thought to be rubies have proved to be red spinel. A gemstone with a similar colour to that of ruby, but easily distinguished using modern instruments. For example, one test would show the stone to be isometric, belonging to the cubic crystal system and singly refractive. Proving that the stone could not be a ruby, as ruby is anisotropic, belonging to the trigonal crystal system and is therefore double refractive. Other tests would confirm the true identity of the red stone. Rubellite (red tourmaline) is a very attractive stone and is also similar in colour to ruby, hence the name, and in good examples could easily be mistaken for ruby.
Ruby is a variety of the species corundum, the other variety is sapphire which occurs in all colours except red, red is reserved for ruby only. It is often difficult to differentiate between a ruby and a pink sapphire. There is no precise demarcation between colours and the human memory is poor at retaining precise colours, without reference colours at hand. The lighting used to illuminate the stone affects the colour drastically. Hence some borderline pink sapphires have been sold as a rubies.
As a mounted gemstone ruby is not prone to damage, at 9 on the Mohs' scale of hardness corundum is a very hard and durable material. Diamond is the only natural material harder than corundum (ruby and sapphire).
Source locations for ruby include: Afghanistan, Australia, Brazil, Cambodia, Madagascar, Myanmar, Pakistan, Thailand and USA.
Properties of the Gemstone and Additional Information
| Gemstone type: | A variety of corundum. The only variety considered red. |
| Crystal System: | Trigonal |
| Chemical Composition: | Aluminium oxide, AL2O3 |
| Colour: | Red, may contain tints of purple, pink or brown. |
| Lustre: | Bright vitreous |
| Pleochroism: | Dichroic: pink-red to orangey-red |
| Dispersion: | Low |
| Hardness: | 9 on the Mohs' scale |
| Toughness: | Excellent |
| Cleavage: | Parting of twin planes may occur (at the interface region, when the intergrowth of crystals has taken place). |
| Density in gm/cc: | 3.8 to 4.05 |
| Double refraction: | Yes |
| Refractive index: | 1.76 to 1.78 |
Common Treatments
Heat treatment is commonly used to improve the colour of ruby. The transparency is also improved by dissolving rutile and silk inclusions at high temperatures and cooling rapidly.
Following treatment the colour remains stable, but heavily included stones may be weakened by the heat process.
Surface reaching cavities may be filled with glass or other materials.
Oiling of cracked stones is carried out to reduce the visibility of the cracks, improving the clarity, colour and therefore general appearance of the stone.
Surface or lattice diffusion of corundum is carried out on pale or near colourless stones of low value. This process applies a layer of colour that just penetrates the stones surface. The treated stone may appear as a fine example of ruby, but re-polishing these stones with abrasive wheels will remove the skin-deep layer thereby removing the colour. Any chipping to the facets, although unlikely, would also show a change of colour.
Beryllium diffusion of corundum is a new concept in ruby and sapphire enhancement. The process creates yellow, orange, red, brown and blue colours from pale or nearly colourless material. It can also change an actual colour and transform dull coloured corundum into vibrant richly coloured material. For example, bluish rubies after diffusion may be a fine red colour. Beryllium diffusion may colour an area close to the surface or may penetrate the entire stone.