From The Gemology Project
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Chemical composition Al2O3
Crystal system Trigonal
Habit Prismatic, tabular
Cleavage None, twinned stones may show parting
Fracture Conchoidal
Hardness 9
Optic nature Uniaxial -
Refractive index 1.762-1.770
Birefringence 0.008-0.010
Dispersion Low, 0.018
Specific gravity 4
Lustre Vitreous to subadamantine
Pleochroism Strong; puplish-red to orangy-red
Untreated 2.7 carat Ruby courtesy of Wild Fish Gems

Ruby is the red variety of the mineral corundum. When corundum occurs in any other color it is referred to as a sapphire. Rubies are mined primarily in Burma, Madagascar, India and Eastern Africa. More important than the gem's locality of origin is the actual color and clarity of the stone. Rubies that are the most valuable will be a dead red in color, without any modifying tones of violet, orange or brown and are transparent in clarity. A fine ruby still commands the highest price of any stone in the world!

The brilliant red color of the ruby has supported many tales. One is that rubies store vast quantities of heat and when placed in water, they will cause the water to boil. Obviously this is an exaggeration, but I know some that swear if you hold a ruby in your left hand, you'll feel bursts of heat. I'm a bit skeptical, so please let me know if you experience this phenomenon. Ruby, none the less, is a powerful stone and has long been considered a magnet for prosperity, attracting abundance both materially and spiritually.


Spectrum of ruby: both natural and synthetic.

Ruby history

The word ruby is derived from the Latin "rubeus", meaning "red".

Ruby mining

The most famous source of fine rubies is Burma, now known as Myanmar. The ruby mines of Myanmar are older than recorded history; Stone Age and Bronze Age mining tools have been found in the mining area of Mogok. Rubies from the legendary mines in Mogok often have a pure red color, which has been described as "pigeon's-blood" although that term is more fanciful than an actual practical standard in the trade today. Myanmar also produces intense pinkish red rubies which are almost electric in color. Many of the rubies from Burma have a strong fluorescence when exposed to ultraviolet rays like those in sunlight.

Ruby phenomena

Star and cat's eye

Inclusion images

The following inclusion images are courtesy of Apsara.

Apatite in untreated Mogok ruby
Apatite in untreated Mogok ruby
Distorted calcite guest crystals in untreated Mogok ruby

Rutile silk in untreated Mogok ruby
Heat treated Mong Hsu ruby
Partially dissolved rutile silk in heat treated Vietnamese ruby

Rounded calcite guest crystals with 'treacle' colour swirls in un-heated Mogok ruby
Growth lines, guest crystals and un-disolved rutile silk in un-heated Mogok ruby
Treacle colour swirls, growth lines and guest crystals in un-heated Mogok ruby

Rounded calcite guest crystals in un-heated Mogok ruby
Unusual acicular guest crystal and small particle inclusions in un-heated Mogok ruby
Distorted calcite guest crystal in un-heated Mogok ruby

Guest crystals in un-heated Mogok ruby
Apatite and calcite guest crystals reflecting within an un-heated Mogok ruby