Corundum
Gemological Note: Red varieties of corundum are known as Ruby. Varieties of corundum possessing any color other than red are collectively referred to as Sapphire.
Corundum
Formula:
Trade Name: Alumina
Color: Colorless, blue, red, pink, yellow, gray, golden-brown
Luster: Adamantine to vitreous, sometimes pearly
Hardness: 9 (Mohs scale)
Specific Gravity: 3.98 – 4.1
Crystal System: Trigonal
Mineral Group: Hematite group
Etymology: The name was first recorded as “corinvindum” by John Woodward in 1725, derived from the Sanskrit word kuruvinda (ruby). The current spelling, “corundum,” was adopted by Richard Kirwan in 1794. In antiquity, the mineral was known by various names, including adamant, sapphire, ruby, hyacinth, and asteria.
Gemological Note: Red varieties of corundum are specifically designated as Ruby, while all other color varieties are referred to as Sapphire.
