Andesine
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| Andesine | |
|---|---|
 Andesine |
|
| General | |
| Category | plagioclase,feldspar,tectosilicate |
| Chemical formula | (Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) is between 30%-50% |
| Identification | |
| Color | White, gray, green, yellow, °esh-red |
| Crystal habit | Crystals rare, to 2 cm; commonly massive or granular |
| Crystal system | Triclinic pinacoidal H-M Symbol (1) |
| Twinning | Common following albite, pericline, and carlsbad twin laws |
| Cleavage | Perfect on {001}, good on {010} |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6 - 6.5 |
| Luster | Subvitreous to pearly |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.66 - 2.68 |
| Optical properties | Biaxial (+/-) |
| Refractive index | nα = 1.543 - 1.554 nβ = 1.547 - 1.559 nγ = 1.552 - 1.562 |
| 2V angle | Measured: 76° to 83° |
| Diagnostic features | Requires optical/chemical analysis |
| References | [1][2][3] |
Andesine is a silicate mineral, a member of the plagioclase feldspar solid solution series. Its chemical formula is (Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% Anorthite) is between 30%-50%.The formula may be written as Na0.7-0.5Ca0.3-0.5Al1.3-1.5Si2.7-2.5O8.[1]
The plagioclase feldspars are a continuous solid solution series and as such the accurate identification of individual members requires detailed optical study, chemical analysis or density measurements.[4]
Andesine was first described in 1841 for an occurrence in the Marmato mine, Marmato, Cauca, Chocó Department, Colombia.[3][2] The name is for the Andes due to its abundance in the andesite lavas in those mountains.[1][4]
Andesine occurs in intermediate igneous rocks such as diorite, syenite and andesite. It characteristically occurs in metamorphic rocks of granulite to amphibolite facies commonly exhibiting antiperthite texture. It also occurs as detrital grains in sedimentary rocks. It is commonly associated with quartz, potassium feldspar, biotite, hornblende and magnetite.[1]
References
- ^ a b c d http://rruff.geo.arizona.edu/doclib/hom/andesine.pdf Handbook of Mineralogy
- ^ a b http://webmineral.com/data/Andesine.shtml Webmineral data
- ^ a b http://www.mindat.org/min-220.html Mindat.org
- ^ a b Klein, Cornelis, and Cornelius S. Hurlbut, Jr., Manual of Mineralogy, Wiley, 20th ed. 1985, p. 455 ISBN 0-471-80580-7
External links
"Andesine". Encyclopædia Britannica (11th ed.). 1911.
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