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Andesine
Chemical Formula	(Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) is between 30%-50%
Species	Silicates
Crystal System	Triclinic
Mohs Scale	6
Specific Gravity	2.66-2.68
Color	White, gray, green, yellow, flesh-red
Streak	White
Luster	Sub-Vitreous, Pearly
Refractive Index	n = 1.543 - 1.554 n = 1.547 - 1.559 n = 1.552 - 1.562
Diaphaneity	Transparent, Translucent
Cleavage	PerfectPerfect on , less perfect on ; also observed.
Fracture	Irregular/Uneven, Conchoidal
Crystal Habit：Crystals rare, to 2 cm; commonly massive or granular
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.

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 Na_0.7-0.5Ca_0.3-0.5Al_1.3-1.5Si_2.7-2.5O₈.

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. Refractive indices and specific gravity increase directly with calcium content.

Name and discovery

Andesine was first described in 1841 for an occurrence in the Marmato mine, Marmato, Cauca, Chocó Department, Colombia. The name is for the Andes due to its abundance in the andesite lavas in those mountains.

Occurrence

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.