Oligoclase - Oligoclase is a rock-forming mineral from the plagioclase subgroup of the feldspar group. Consists of 10-30% anorthite and 90-70% albite. Included in many breeds. Characteristic of acidic igneous rocks and many metamorphic rocks.
You can see oligoclase stone for sale and buy it in the Minerals of Russia online store.
Category | plagioclase, feldspar, tectosilicate |
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Formula (repeating unit) |
(Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% anorthite) is between 10%–30% |
Crystal system | Triclinic |
Crystal class | Pinacoidal (1) (same H-M symbol) |
Identification | |
Color | usually white, with shades of grey, green, or red |
Cleavage | Perfect {001}, Good {010} , Poor {110}. |
Fracture | Uneven, Sub-Conchoidal |
Mohs scale hardness | 6 to 6.5 |
Luster | Vitreous |
Streak | White |
Specific gravity | 2.64 to 2.66 |
Refractive index | nα=1.533–1.543; nβ=1.537–1.548; nγ=1.542–1.552 |
Birefringence | 1st order |