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Albite

Class: Silicates
Group: Feldspar

Varieties | Names:

A major constituent of granites and granite pegmatites, basalts, and in hydrothermal and alpine veins; a product of potassium metasomatism in some schists (Anthony et al., 2001—2005).
Andesine — specimen 0305
Andesine — specimen 0305, photo © NMNHS

Original description: ‘Albit’ Gahn, J. G., Berzelius, J., 1815. Underfökning af nagra i grannskapet af Fahlun funna Fossilier — Afhandlingar i Fysik, Kemi och Mineralogi 4: 180—181 [view in ‘Library’].

Type locality: Finnbo, Falun, Dalarna, Sweden.

Type material: unknown.

Etymology: from the Latin albus, for white, its characteristic colour.

Distribution: Austria: Zillertal, Tirol; Brazil: Minas Gerais; Canada; France; Italy; Russia: Ural; Switzerland; USA (Anthony et al., 2001—2005).

Chemistry

NaAlSi3O8

Essential elements: oxygen (O), sodium (Na), aluminium (Al), silicon (Si).

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: crystals commonly tabular, may be curved, to 3 cm; divergent aggregates, granular, cleavable massive. Twinning: common around [010]; many other laws (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {001}, very good on {010}, imperfect on {110} (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6—6.5 (Lazzarelli, 2012). Density: 2.6—2.65 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: white to grey, bluish, greenish, reddish (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.525—1.542 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.008—0.011. Dispersion: weak (Anthony et al., 2001—2005). Pleochroism: none.

Material from ‘Repository’

18 specimens: 0305 — 0.41 ct, no locality data; 0306 — 0.41 ct, no locality data; 0129 — 0.43 ct, no locality data; 0410 — 0.42 ct, no locality data; 0331 — 1.34 ct, Democratic Republic of the Congo; 0320 — 1.28 ct, Democratic Republic of the Congo; 0726 — 0.44 ct, no locality data; 0727 — 0.41 ct, no locality data; 0267 — 1.54 ct, no precise locality [Africa]; 0342 — 1.57 ct, no precise locality [Africa]; 0345 — 5.90 ct, Democratic Republic of the Congo; 0278 — 0.76 ct, no precise locality [Africa]; 0349 — 2.35 ct, no precise locality [Africa]; 0072 — 0.96 ct, Madagascar; 0274 — 1.61 ct, Madagascar; 0285 — 0.96 ct, Madagascar; 0622 — 6.63 ct, no precise locality [Africa]; 0623 — 7.49 ct, no precise locality [Africa].


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