Zoisite
Species
Uncommon · Ca₂Al₃(SiO₄)(Si₂O₇)O(OH)
A calcium aluminium silicate of the epidote group, common in the schists of medium-grade metamorphism and in eclogites. Its crystals are deeply striated prisms. The blue to violet gem of the Merelani Hills in Tanzania is its variety tanzanite. Named for Baron Siegmund Zois, who supplied the first specimens.
Identity
Crystallography
- Crystal system
- Orthorhombic
- Habits
- Prismatic, Columnar, Massive
- Fracture
- Uneven
Physical properties
- Mohs hardness
- 6.5
- Density
- 3.3 g/cm³
- Luster
- Vitreous, Pearly
- Colors
- white, gray, green, pink, blue, purple, brown
- Streak
- white
- Transparency
- Transparent, Translucent
Geology
- Origins
- Metamorphic
- Host rocks
- Schist and gneiss
- Associated minerals
- Garnet, Albite, Hornblende, Quartz, Calcite
- Geography
- Tanzania (Merelani Hills), Austria (Saualpe, Zillertal), Norway (Trondheim), Pakistan (Shigar Valley), USA
Classification
- Rarity
- Uncommon
- Gem quality
- Yes
Sources
- M. Pasero and others, IMA Commission on New Minerals, Nomenclature and Classification, The New IMA List of Minerals, updated September 2026. International Mineralogical Association (CNMNC), 2026.
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Zoisite. Mineral Data Publishing, Handbook of Mineralogy, 2001.
- Zoisite. Mindat.org (Hudson Institute of Mineralogy).
- Tanzanite. Mindat.org (Hudson Institute of Mineralogy).
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