Zoisite

Zoisite is a member of the Epidote mineral group that includes Allanite, Clinozoisite, Epidote, Hancockite, Mukhinite, Piedmontite, Tanzanite, Thulite and Zoisite. The Chemical Formula of Zoisite is Ca₂Al₃Si₃O₁₂(OH) [Calcium Aluminum Silicate Hydroxide] and its molecular weight is 454.36 gm. Moh’s Hardness of Zoisite is 6.0 – 7.0. 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. Zoisite has a specific gravity of 3.15 – 3.36 (g/cm3) and the refractive index of 1.685 – 1.725 Biaxial ( + ). 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.

Category:	Sorosilicate – epidote group
Chemical Formula:	Ca2Al3Si3O12(OH)
	[Calcium Aluminum Silicate Hydroxide]
Molecular Weight:	454.36 gm
Composition:	Calcium 17.64 % Ca 24.68 % CaO   Aluminum 17.82 % Al 33.66 % Al2O3   Silicon 18.54 % Si 39.67 % SiO2   Hydrogen 0.22 % H 1.98 % H2O   Oxygen 45.78 % O         100.00 %   100.00 % = Total Oxide

 

Crystallography:	Orthorhombic – Dipyramidal
Crystal Habit:	Crystals prismatic, to 10 cm, typically deeply striated and poorly terminated; columnar to compact, massive.
Twinning:	None

 

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

 

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