Physical Properties of Rubies & Sapphires

Find out the about the chemical composition of rubies & sapphires...

Ruby Crystals

Rough ruby crystals offered for sale.

Sapphire Crystals

Freshly recovered corundum crystals being sorted.

Sapphire Crystals

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

Image

A rough ruby crystal.

Apsara - Rubies & Sapphires

Dealers of fine quality rubies, sapphires and other coloured gems.

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