Zoisite is named for the famed collector Sigmund Zois. Discovered in Austria in 1805 in the Sau-Alp mountains, zoisite was not always considered gem material. A green specimen with hornblende inclusions and, more importantly, large opaque ruby inclusions, was discovered in 1954 making zoisite interesting for ornamental objects and some gem usage.

A major variety of zoisite is tanzanite, a blue or violet colored gem, discovered in 1967.

Another variety of zoisite is Thulite, an opaque red stone often confused with rhodonite.


Thulite (Green) with Ruby (Red)

Gemological Information for Zoisite

Color: Blue to Violet, Brown, Green-Yellow and Pink
Crystal Structure Orthorhombic
Refractive Index: 1.691 to 1.700
Durability: Fair to Poor
Hardness: 6 to 7
Family: Zoisite
Similar Stones: Rhodonite, Hydrogrossular Garnet, Sapphire, Benitoite, Spinel, Iolite
Treatments: Heating
Country of Origin: Tanzania (Tanzanite), Austria, Germany, Italy, Mexico, Switzerland, U.S.

Zoisite Care

Ultrasonic Cleaning: Never
Steam Cleaning: Never
Warm Soapy Water: Safe
Chemical Attack: Hydrochloric and Hydrofluoric Acids Attack
Light Sensitivity: Stable
Heat Sensitivity: Jeweler's Torch may Fuse


  • Gem Reference Guide, Los Angeles: Gemological Institute of America, 1988. Pp. 262-264.
  • Schumann, Walter. Gemstones of the World, New York: Sterling Publishing, Co., 1977. Pp. 160.