Albite: Gemstone Information
Found widely in greenschist facies metamorphic rocks. In igneous rocks, it occurs principally in pegmatites and in alkali-rich rocks such as nepheline syenites and other feldspathoidal types. Common in spilites and keratophyres.
Albite occurs throughout the world, with major locations in the Alps, Urals, Harz Mountains, France, Norway, Madagascar and the USA (Maine, Virginia, Colorado). Gems are normally 3 cts.
Opaque to translucent, rarely transparent. Simple and polysynthetic twinning are ubiquitous, the latter producing fine striations on surfaces.
Lustre: Vitreous to pearly
• Colour: Usually white, rarely colourless or pale shades of blue, green, pink–orange, reddish or brown. The colour of some bluish green albite-oligoclase material is attributed to Pb and OH involving radiation- induced transitions
• Varieties: (see also moonstone) Maw-sit-sit is a rock mainly composed of albite with lesser amounts of Cr-pyroxenes and Cr-amphiboles: RI = 1.54, SG = 2.7. It is named after the locality of origin in Myanmar. Peristerite is the name given to iridescent albite-oligoclase lamellar intergrowths (see also peristerescence and moonstone). The most beautiful peristerite is said to be found at Monteagle, Hastings County, Ontario, and this material has been fashioned into beads and cabochons. An ivory-white peristerite is found in some quantity in the Villeneuve mine, Labell County, and at Buckingham, Quebec. Also found at various other localities in Ontario. Platy albite is called cleavlandite.
• Crystal system: Triclinic
• Refractive index: α 1.528–1.533; β 1.532–1.537; γ 1.538–1.542 (Madagascar α 1.530–1.531; β 1.532–1.533; γ 1.539–1.540)
• Birefringence: Weak; 0.009–0.010
• Density: 2.61–2.63 (Madagascar 2.62)
• Hardness: 6
• Dispersion: Weak
• Cleavage/fracture: Perfect to excellent prismatic cleavages in two directions/ brittle with a conchoidal to uneven fracture
• Fluorescence: SWUV – white, green, LWUV – green (peristerite – very weak brown fluorescence under both LWUV and SWUV)
• Phosphoresence: Golden brown, green
• Inclusions: (see moonstone)
• Optical effects: chatoyancy, asterism, colour change, ADR (see moonstone) Cat’s eye gems around 50 cts are known
• Treatment: Irradiation may turn colourless material blue if lead and water impurities are present (see amazonite).