Belomorite

Belomorite
Belomorite (Karelia, Chupinskaya Bay)
General
Category	Plagioclase (peristerite)[1]
Formula (repeating unit)	Na[AlSi3O8] or (Na,Ca)(Si,Al)4O8
Crystal system	triclinic
Identification
Color	light: white with a bluish tint, grayish, greenish
Crystal habit	granular masses or massive aggregates
Cleavage	perfect by {001}
Fracture	uneven, conchoidal
Tenacity	very brittle
Mohs scale hardness	6–6.5
Luster	glass, pearl with iridescence
Streak	white
Diaphaneity	translucent to opaque
Density	2.64-2.66 (calculated)

Belomorite (Russian: Беломори́т — from the toponym),^[2] sometimes peristerite or moonstone, also murchisonite, Ceylon opal, hecatolite — a decorative variety of albite (oligoclase) of white or light gray color with a distinct iridescence effect. By composition, belomorite belongs to the feldspar family; it is a sodium aluminosilicate from the plagioclase group, in most cases belonging to the isomorphic series albite (Ab) — anorthite (An) with an approximate percentage of 70Ab-30An.

The name “belomorite” was given to this variety of albite by academician Alexander Fersman in 1925, based on the location of its discovery near the shore of the White Sea, and also by association — for the similarity of iridescence colors with the shades of sea water. The best varieties of belomorite are translucent or transparent, they have a pearl-glass luster and iridescence in blue, gray-blue, violet-blue, greenish-blue or pale violet tones. The most famous deposits of this gem are in the north, in the pegmatites of the Kola Peninsula and Karelia.

Belomorite is a spectacular and popular jewelry and ornamental material, one of the varieties of moonstone. However, due to its fragility and perfect cleavage, the mineral often breaks and is difficult to process, so it is cut in the form of simple cabochons (oval, round, teardrop-shaped), as well as balls or polished plates.