From The Gemology Project
Revision as of 01:39, 17 August 2012 by RWH (talk | contribs) (Occurrence)
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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
3.30 ct heated Mong Hsu ruby
Photo by Jeff Scovil
Courtesy of R.W. Wise Goldsmiths

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 pure 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.

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



Spectrum of ruby: both natural and synthetic.


  • Asterism
  • Chatoyancy
  • Trapiche


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. Fine rubies are also found in Myanmar at Mong ('Maing') Hsu and at Nanyazeik (Namya).
Much lesser known are deposits of ruby found in Afghanistan. Although reports of rubies mined in Afghanistan were first chronicled by Marco Polo, the mines have long been shrouded in secrecy and mystery. The mines he referred to are for "balas rubies" (spinels). The actual locality is at Kuh-i-Lal in present-day Tajikistan, just opposite the Afghan border.

Ruby from Afghanistan

The crystal on the left, is semi-translucent and heavily included. It can be described as a subhedral ruby crystal nestled in a matrix of white calcite/dolomite marble, dotted with pseudo-hexagonal books of muscovite. It is very strongly fluorescent displaying bright red with LWUV, and weaker red with SWUV.

True rubies are found in Afghanistan at Jegdalek, east of Kabul, which is located in a continental collision zone between the Asian and Indian plates. The deposits occur in metamorphosed limestone (marble) which are found on both plates.
Next to Myanmar, the most important historic source of ruby is Sri Lanka. In modern times, fine rubies have been found along the Thai/Cambodian border between Chanthaburi (Thailand) and Pailin (Cambodia). These deposits were the most important in the world between about 1965 and 1995. Today they are exhausted.
An additional source of ruby is Vietnam. Fine stones have been found at both Quy Chau (along the Lao border) and Yen Bai, north of Hanoi.
East Africa has been a major source of ruby since the 1960's, with a number of sources existing in Kenya, Tanzania and Mozambique. In addition, Madagascar has a number of ruby deposits of varying importance.

Synthesizing Methods

  • Flame Fusion
  • Flux melt (Chatham, Ramaura)
Flux grown synthetic Ramaura ruby, displaying hexagonal patterns and flux relics.
Photo courtesy of Alberto Scarani

  • Czochralski pulling process
  • Float zone method

Inclusion images

Apatite in untreated Mogok ruby
Photo courtesy of
Apatite in untreated Mogok ruby
Photo courtesy of
Distorted calcite guest crystals in untreated Mogok ruby
Photo courtesy of

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

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

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

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


Common enhancements to rubies:

  • Fracture filling - oil, wax or plastic (with dye or without)
  • Lead glass filling - removes crack increases weight
Natural ruby, displaying a surfacing area of glass filling with bubbles
Photo courtesy of Alberto Scarani
Blue flashes in a glass filled ruby, diagnostic for lead-glass filing.
© Tim Spauwen

  • Diffusion treated - heating causing layer on cut stones - enhance color or produce asterism
  • Heat treatment - improves or even changes the color, reduces silk and other impurities