Mineral description : Andesine

Andesine around a corundum crystal. From Södra yxesjön, Värmland.

Mineral class	Silicates : Tektosilicates : Feldspar group.
Chemical formula	(Na,Ca)(AlSi3O8) (70-50% Na, 30-50% Ca)
Crystal system	Triclinic.
Habitus	Tabular to prismatic, commonly with polysyntetic twinning.
Cleavage	[001] Perfect, [010] good, 90 degrees angle. Uneven fracture.
Hardness	6-6.5
Density	2.67-2.69
Color	White to grayish.
Streak	White
Luster	Vitreous.
Description	Andesine is a member of the plagioclase feldspar series.
Occurance	A common part of many rocks, main part of diorites, amfibolite and porphyrite. Rarely in pegmatites.
Associates
Notes	Twinning often produces many layers on top of each other, each only a fraction of a mm to several mm thick. Theese layers can be seen as striations not only on the surface of the crystal, but also on cleavages. This is a characteristic sign of the plagioclase feldspar series.
Locations	A very common mineral. Kärringbricka, Västerfärnebo, Västmanland. In a strange pegmatite together with schorl.

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