Victorian Cat's-Eye Orthoclase Feldspar and Diamond Earrings.
Photo Courtesy of Lang Antiques.

Feldspar is a gem group that includes microcline, orthoclase and plagioclase varieties. Each variety varies as to crystal structure, refractive index, color and other specifics. Gemstones include: amazonite, moonstone, labradorite, sunstone. From the Greek word klasis meaning cleaving (clase) with a cleavage direction as the prefix.

Gemological Information For Feldspar

Color: Light Green, Greenish Blue, White for Microcline, Green, Colorless, White, Yellow, Brown, Gray and Black for Orthoclase, Gray to Black for Labradorite, Orange, Brown, Colorless for Oligoclase
Crystal Structure Triclinic (microcline) Monoclinic (orthoclase and plagioclase)
Refractive Index: 1.522 to 1.530 (microcline) 1.518 to1.526(orthoclase) 1.599 to 1.568 Labradorite, 1.537 to 1.547 Oligoclase
Durability: Poor
Hardness: 6 to 6.5
Similar Stones: Aventurine Quartz, Chalcedony, Turquoise
Treatments: Wax Impregnation, Irradiation
Country of Origin: Worldwide Deposits

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.