
Rough ruby crystals offered for sale.

Freshly recovered corundum crystals being sorted.

Blue sapphire crystals from the Baw Mar mine in Kyatpyin, Mogok.
Properties of Rubies & Sapphires
The word corundum originates from the Sanskrit word kurivinda. Corundum is a mineral to which both rubies and sapphires belong. The chemical composition of corundum is aluminium oxide (Al2 O3) with traces of various transition elements such as chromium (Cr). It is these transition elements that are responsible for producing the stone's colour. Chromium produces the finest red colour in rubies and also pink coloured sapphires. Chromium produces some of the finest colours found in many other gems like emeralds, jadeite, and chrome diopside to name a few. Other transition elements found in corundum include iron (Fe), vanadium (V) and titanium (Ti). Gem quality corundum comes in all colours with red corundum described as ruby and all other colours described as a sapphire with the name of the colour as a prefix. Corundum crystallizes in a hexagonal (trigonal) form with the six crystal faces meeting at 120 degrees.
Refractive Index
Birefringence
Crystal System
Optic Character
Specific Gravity
Hardness
Pleochroism
Chemical Composition
Cleavage
Dispersion
-
-
-
-
-
-
-
-
-
-
1.762 - 1.770
0.008 - 0.009
Hexagonal (trigonal)
Uniaxial (-)
3.97 - 4.03
9
Very Pronounced
Aluminium Oxide
None
0.008

A rough ruby crystal.