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Mineral class | Silicates : Tektosilicates : Feldspar group. |
Chemical formula | (Na,Ca)(AlSi3O8) (100-90% Na, 0-10% Ca) |
Crystal system | Triclinic. |
Habitus | Tabular to prismatic, commonly with polysyntetic twinning. Often occuring in lamellar aggregates (cleavelandite) or as grainy aggregates (albitite). |
Cleavage | Perfect in one direction and good in another with 90 degrees angle. Often with fine striation on cleavages. |
Hardness | 6-6.5 |
Density | 2.62 |
Color | White to colorless. |
Streak | White |
Luster | Vitreous to pearly. Transparent to translucent. |
Description |   |
Occurance | As a major part of many rocks, especially igneous rocks as granites, syenites and 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.
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To silicate index. |
Mineral group index. |
Main index. |
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