Sardonyx is a brown and white banded variety of onyx primarily used in the glyptography.

Gemological information

Gemological Information for Sardonyx
Color	Brown and White Layers
Crystal Structure	Hexagonal (trigonal)
Refractive Index	1.535 to 1.539
Durability	Good
Hardness	6.5 to 7
Similar Stones	Dyed Onyx
Treatments	Dyeing, Heating
Country of Origin	Brazil
Sardonyx Care
Ultrasonic Cleaning	Usually Safe (watch for glued together white and brown cameo imitiations)
Steam Cleaning	Usually Safe
Warm Soapy Water	Safe
Chemical Attack	Attacked by Hydrofluoric Acid and Nitric Acid may remove dye
Light Sensitivity	Stabke
Heat Sensitivity	May Alter Color

Sources

Gem Reference Guide, Los Angeles: Gemological Institute of America, 1988. Pp. 45-48.

Newman, Harold. An Illustrated Dictionary of Jewelry, New York: Thames and Hudson, 1981. Pp. 269.

Schumann, Walter. Gemstones of the World, New York: Sterling Publishing, Co., 1977. Pp. 142.