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Zoisite
Current inventory:  1 gem
 

   
Zoisite is named after Siegmund Zois, Baron von Edelstein (1747-1819), Austrian scholar who financed mineral-collecting expeditions.

Discovered in 1805;   IMA status: Valid (pre-IMA; Grandfathered).

Chemistry

Chemical Formula:

Ca₂Al₃Si₃O₁₂(OH)

[Calcium Aluminum Silicate Hydroxide]

Molecular Weight:

454.36 gm

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/C.23-100

Nickel-Strunz 10th Ed. ID:

9.BG.10

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordination

Related to:

Epidote Group. The orthorhombic dimorph of Clinozoisite. The only orthorhombic member of the Epidote Group.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals prismatic, to 10 cm, typically deeply striated and poorly terminated; columnar to compact, massive.

Twinning:

None

Physical Properties

Cleavage:

[010] Perfect, [100] Imperfect

Fracture:

Uneven, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0 - 7.0

Density:

3.15 - 3.36 (g/cm³)

Radioactivity:

Not Radioactive

Optical Properties

Color:

Green, Brown, Blue (Tanzanite), Purple, Pink, Rose red (Thulite), Gray

Transparency:

Transparent to Translucent

Luster:

Vitreous, Pearly

Refractive Index:

1.685 - 1.725  Biaxial ( + )

Birefringence:

0.006 - 0.018

Dispersion:

Relatively Strong

Pleochroism:

X = pale pink to red-violet; Y = nearly colorless to bright pink or deep blue; Z = pale yellow to yellow-green

Occurances

Geological 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.

Common Associations:

Albite, Biotite, Calcite, Garnet, Hornblende, Quartz

Common Impurities:

Fe, Mn, Mg, Cr, Ti, Ca, Na, V, Sr, H₂O

Type Locality:

Prickler Halt, Ladinger Spitze Mt. - Speikkogel Mt. area, Saualpe Mts, Carinthia, Austria

Year Discovered:

1805

View mineral photos:

Zoisite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Zoisite is a member of the Epidote mineral group that includes Allanite, Clinozoisite, Epidote, Hancockite, Mukhinite, Piedmontite, Tanzanite, Thulite and Zoisite. Actually, Tanzanite and Thulite are types of Zoisite. Zoisite is the only orthorhombic member of the Epidote group. Zoisite is typically found in various shades of green and brown. Tanzanite is the fine gem variety of Zoisite that has been heated and turned to the popular blue and purple colors. Thulite is the pink to dark pink variety of Zoisite. Tanzanite is by far, the most popular and well known variety of the Epidote mineral group thanks to its eye-catching blue and purple colors.
 

  
Zoisite gems for sale: