Opal

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.