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Prehnite


Properties
Chemical Composition: 
Calcium Aluminium Silicate Ca2Al2Si3O10(OH)2
Classification / Type: 
-
Colors / Varieties: 
Green, yellow-brown, yellow-green. Transparency: Translucent to Opaque. Chatoyant variety.
Crystal System / Forms: 
Orthorhombic System / Aggregates with botryoidal habit.
Hardness: 
6
Specific Gravity: 
2.80 - 3.00
Cleavage / Fracture: 
Not Visible / Splintery fracture.
Optic Character: 
Anisotropic, D.R.; Aggregate (A.G.G.)
Lustre: 
Vitreous to greasy
Refractive Index / Birefringence: 
1.615 - 1.650 / 0.035
Pleochroism: 
None.
Dispersion: 
-
Magnification: 
Fibrous structure with radiating pattern, banding.
U.V. Fluorescence: 
Brownish yellow
Spectrum: 
Not Diagnostic.
Cause of Color: 
Iron
Treatment (Enhancement): 
-
Specific Tests & Remarks: 
Consist of fibers in radiating manner in different planes.
Synthesis: 
-
Simulants (with key separation tests): 
Jadeite (R.I., S.G., structure, spectrum), Serpentine (R.I., S.G., lustre, hardness), Idocrase (R.I., spectrum, structure), Hydrogrossular Garnet (R.I., S.G.), Aventurine Quartz (R.I., S.G., structure, spectrum), Maw-sit-sit (color, structure), Aragonite (R.I., birefringence, structure).
Geological Occurrence: 
In cavities of volcanic rocks.
Sources: 
U.S.A., France, Scotland, Australia, China.
Cuts & Uses: 
Cabochons, beads, carvings, etc.
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