Andesine

Formula: (Na,Ca)(Si,Al)4O8
System:  Triclinic   
Colour: White, gray, green, ...
Lustre:  Sub-Vitreous, Pearly   
Hardness: 6 - 6½
Member of: Feldspar Group
Name: For the Andes Mountains of South America where it is abundant in the lavas.

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Occurrences of Andesine

Geological Setting:  Widespread in igneous rocks of intermediate silica content, as syenites and andesites. Characteristic of granulite to amphibolite facies metamorphism, commonly as antiperthite; as detrital grains in sedimentary rocks.

Physical Properties of Andesine

Lustre:  Sub-Vitreous, Pearly
Diaphaneity (Transparency):  Transparent, Translucent
Colour: White, gray, green, yellow, flesh-red.
Streak: White
Hardness (Mohs): 6 - 6½
Tenacity:  Brittle
Cleavage:  Perfect
Perfect on {001}, less perfect on {010}; {110} also observed.
Fracture:  Irregular/Uneven, Conchoidal

Crystallography of Andesine

Crystal System:  Triclinic

Chemical Properties of Andesine

Formula: (Na,Ca)(Si,Al)4O8
Essential elements: Al, Na, O, Si
All elements listed in formula:    Al, Ca, Na, O, Si

Photo:

This gem is 8.04 carats and is from Nyma, Tibet. The sample is on display at the Smithsonian Museum of Natural History.

Berry Ledge locality, Cornish, York Co., Maine, USA
© 2006 Peter Cristofono

More Info >> Mindat: Andesine

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Posted in: Minerals