Prehnite

Prehnite is a beautiful gem with a pearly to velvety look that glows with color in well faceted gems. The chemical formula of Prehnite is Ca₂Al₂Si₃O₁₀(OH)₂ (Calcium Aluminum Silicate Hydroxide) and its molecular weight is 395.38 gm. Most facetable material is found in Australia and Mali. Prehnite has a specific gravity of 2.80 – 2.95 (g/cm3) and the refractyive index of 1.611 – 1.665 Biaxial (+). Moh’s Hardness of Prehnite is 6.0 – 6.5. The richest, most saturated colors come from Australia. When coming to crystal habit is Uncommon as crystals, tabular or prismatic to steep pyramidal, to 4.5 cm. Aggregates are fanlike, reniform, globular, stalactitic; granular, compact. Colors range from bright yellow (Australia), yellowish green, pale green (Mali) and colorless.

Category:	Silicate mineral
Chemical Formula:	Ca2Al2Si3O10(OH)2
	Calcium Aluminum Silicate Hydroxide
Molecular Weight:	395.38 gm

Composition:	Calcium	20.27 %	Ca	28.37 %	CaO
	Aluminum	13.65 %	Al	25.79 %	Al2O3
	Silicon	21.31 %	Si	45.59 %	SiO2
	Hydrogen	0.25 %	H	2.28 %	H2O
	Oxygen	44.51 %	O
		100.00 %		100.00 %	= TOTAL OXIDE

 

Crystallography:	Orthorhombic – Pyramidal
Crystal Habit:	Uncommon as crystals, tabular or prismatic to steep pyramidal, to 4.5 cm. Aggregates are fanlike, reniform, globular, stalactitic; granular, compact.
Twinning:	Fine lamellar

 

Cleavage:	Good on [001], Poor on [110]
Fracture:	Irregular/Uneven
Tenacity:	Brittle
Moh’s Hardness:	6.0 – 6.5
Density:	2.80 – 2.95 (g/cm3)
Luminescence:	Fluorescent; blue white or mild peach under SW UV, yellow under LW UV
Radioactivity:	Not Radioactive

 

Color:	Colorless, light to dark Green, Yellow, White, Gray
Transparency:	Semitransparent to Translucent
Luster:	Vitreous to Pearly; Pearly on cleavage {001}
Refractive Index:	1.611 – 1.665  Biaxial ( + )
Birefringence:	0.0220 – 0.0330
Dispersion:	Weak; r > v
Pleochroism:	None

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