Albite
Structure : TriclinicHardness : 6
Specific Gravity : 2.64
Refractive index : 1.54 - 1.5
Doubly Refracting (bi-refraction) : 0.009
Albite is an alkali feldspar mineral. It is the sodium end member of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite end member has the formula NaAlSi3O8. It is a tectosilicate.
Albite crystallizes with triclinic pinacoidal forms. Its specific gravity is about 2.62 and has a Mohs hardness of 6. Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling. It occurs in granitic and pegmatite masses and also in some hydrothermal vein deposits.
It was first reported in 1815 for an occurrence in Sweden. The name is from Latin, albus for the typical white color.
Hardness: 6-6.5
- Albite Chemical composition: NaAlSi3O8
- Class: tectosilicate
- Crystal system: triclinic; bar 1
- Crystal habit: commonly tabular parallel to {010}, also can be blocky, massive or form as platy crystals in the albite variety clevelandite.
- Twinning: commonly shows polysynthetic lamellar twinning according to the albite twin law {010}, sometimes visible to the unaided eye as striations on {010}.
- Specific gravity: 2.62
- Index of refraction: 1.53
- Birefringence: weak maximum birefringence of 0.010
- Pleochroism: colorless in section
- Hardness: 6
- Color: usually white, rarely colorless or pale shades of blue, green, pink-orange or brown
- Luster:vitreous
- Transparency: opaque to translucent, rarely transparent
- Cleavage: characteristic cleavages are {001} perfect, {010} distinct
- Fracture: conchoidal to uneven
- Streak: white