Plagioclase is a sub-series of the feldspar group.

Gemological information

Gemological Information for Feldspar
Color Gray to Black for Labradorite, Yellow, Orange to Brown for Oligolcase
Crystal Structure Monoclinic
Refractive Index 1.599 to 1.568 Plagioclase
Durability Poor
Hardness 6 to 6.5
Similar Stones Beryl, Quartz, Scapolite, Goldstone Glass
Treatments Wax Impregnation, Irradiation
Country of Origin Brazil, Madagascar, Norway, US, Russia
Feldspar Care
Ultrasonic Cleaning Never
Steam Cleaning Never
Warm Soapy Water Safe
Chemical Attack Hydrofluoric Acid attacks quickly. Impurities may react to other acids
Light Sensitivity Stable
Heat Sensitivity Can Crack, Fade and Cleave


Gem Reference Guide, Los Angeles: Gemological Institute of America, 1988. Pp. 101-107.

Newman, Harold. An Illustrated Dictionary of Jewelry, New York: Thames and Hudson, 1981. Pp. 122.

Schumann, Walter. Gemstones of the World, New York: Sterling Publishing, Co., 1977. Pp. 164-167.