Mineral Information and Data:

Zoisite
Ca2Al3(Si2O7)(SiO4)O(OH) [CNMNC approved formula]

Named after the Austrian natural scientist, Siegmund Zois (1747-1819).

IMA status : Valid species (Pre-IMA 1805) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
58.02.01b.01  
  (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups
  (58.02) with cations in [6] and higher coordination; single and double groups (n=1,2)
  (58.02.01b) Epidote group (Zoisite subgroup)
  
Nickel-Strunz
(10th edition) :
09.BG.10
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BG) Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Space group: Pnma
Unit cell: a = 16.1909(15)Å, b = 5.5466(5)Å, c = 10.0323(6)Å, Z=4
Crystal Habit: Crystals prismatic, to 10 cm, typically deeply striated || [010] and poorly terminated; columnar to compact, massive.
  
Color: White, gray, greenish brown, greenish gray, pink, blue, purple; colorless to pink in thin section
Diaphaneity: Transparent to translucent
Luster: Vitreous, pearly on cleavage
Hardness (Mohs): 6 - 7
Measured Density: 3.15 - 3.36 g/cm3
Cleavage: {010}, perfect; {100}, imperfect
Tenacity: Brittle
Fracture: Uneven, conchoidal
  
Polymorphism and Series: Dimorphous with clinozoisite.
Geologic Setting: Typically in medium-grade regionally metamorphosed crystalline schists formed from igneous, sedimentary, or metamorphic rocks relatively high in calcium; in eclogites and blueschist facies metamorphic rocks.
Mineral Association: Garnet, albite, biotite, "hornblende", quartz, calcite
  
Other Properties: Gemstone Readily Available.

 

Zoisite
Origin: Alchuri, Baltistan, Pakistan
Sample size: 2.3 x .9 x .8 cm
Photo: Rob Lavinsky

 

Zoisite
Grey-green cm-sized zoisite crystals (not terminated) in quartz matrix
Origin: Valley of the Jerisjokk upper course,
Overuman-Tärnasjön, Lapland, Sweden
Sample size: 3 x 4 cm
Photo: Diederik Visser

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