ALBITE

    Class : Silicates
    Subclass : Tectosilicates
    Crystal System : Triclinic
    Chemistry : NaAlSi3O8
    Rarity : Very common

Albite is the sodic term for plagioclase feldspars, a major subgroup of silicates ranging from albite (sodium) to anorthite (calcium). Its name comes from the Latin albus (white) in reference to its color. It can also sometimes be gray with greenish or bluish reflections, more rarely reddish. It usually accompanies quartz, micas, orthoclase or microcline, oligoclase, and many other minerals. Albite is one of the essential constituents of granites and pegmatites associated with them, but also of diorites and nepheline syenites (of which it is the only feldspar). It is also abundant in metamorphic rocks of low pressure and low temperature (greenschist facies), it is common in alpine clefts, and frequent in hydrothermal alteration zones of metalliferous deposits : it is one of the minerals most abundant in the earth's crust. Well-formed single crystals are relatively rare. Its habitus is generally tabular, sometimes elongated with very widespread polysynthetic twins ; it often constitutes, especially in pegmatites, aggregates of lamellar crystals known under the name of cleavelandite. Albite is sometimes used in the ceramic and porcelain industry, it can also be cut for jewelry.

Albite from St-Véran, Hautes-Alpes, France
Albite on tourmaline from Stak Nala, Pakistan
Cleavelandite on tourmaline from Stak Nala, Pakistan
Albite on tourmaline and quartz from Stak Nala, Pakistan

Albite in the World

Albite is present in many deposits, the most beautiful specimens are well-formed decimetric crystals, extracted from the alpine clefts of the Swiss Alps (St-Gothard) and Italy (Val di Vizze and Valle Aurina, where they measure up to 30cm). Excellent crystals come from Italian pegmatites (Baveno, Piedmont) and Pakistani deposits (Dusso). Magnificent lamellar crystals (cleavelandite variety) come from the Brazilian pegmatites of Minas Gerais (Divino das Laranjeira, Galiléia...) and from the pegmatitic fields of California (Pala, Mesa Grande).

Albite in France

In France, superb albite crystals come from the alpine fissures St-Christophe-en-Oisans (Isère) and St-Véran (Hautes-Alpes), see main photo.

Twinning

The twins are common around [010] or perpendicular to {010}, giving polysynthetic streaks on {001} or {010} ; many other single and multiple contact twins.

Fakes and treatments

No fake reported for this mineral species.



Hardness :  6 to 6.5
Density : 2.6
Fracture : Irregular to conchoidal
Trace : White




TP : Translucent to transparent
RI : 1.528 to 1.542
Birefringence : 0.010
Optical character : Biaxial +
Pleochroism : None
Fluorescence : Yellow to red


Solubility : Hydrofluoric acid

Magnetism : None
Radioactivity : None