Formula: SiO2 · nH2O
Color: Colorless, white, yellow, red, orange, green, brown, black, blue
Shine: Glassy, waxy, greasy, dull
Hardness: 5½ - 6½
Specific gravity: 1.9 - 2.3
Name: the origin of the name is uncertain. It can be from Sanskrit "upala", meaning "stone" or "precious stone" or from opal, the ancient Latin name for the jewel.