Corundum

Sapphire

Gem gravels, Ratnapura, Ratnapura District, Sabaragamuwa Province, Sri Lanka

Ruby

Mysore District, Karnataka, India

Ruby

Mysore District, Karnataka, India

Formula:

Al2O3

System:

Trigonal

Colour:

Colourless, blue, red, ...

Hardness:

9

Member of:

Hematite Group

Name:

Named "corinvindum" in 1725 by John Woodward and derived from the Sanskrit, kuruvinda ("Ruby"). Richard Kirwan used the current spelling "corundum" in 1794. Known by many names in ancient times: adamant, sapphire, ruby, hyacinthos, asteria, etc.

The aluminum analogue of Eskolaite, Hematite, and Karelianite.
The red (Cr-bearing) gem variety is called Ruby.
The blue (Fe- and Ti-bearing) gem variety is called Sapphire.