Scapolite


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scapolite

[′skap·ə‚līt]
(mineralogy)
A white, gray, or pale-green complex aluminosilicate of sodium and calcium belonging to the tectosilicate group of silicate minerals; crystallizes in the tetragonal system and is vitreous; hardness is 5-6 on Mohs scale, and specific gravity is 2.65-2.74. Also known as wernerite.

Scapolite

 

a group of silicate minerals consisting of the solid-solution series 3NaAlSi3O8 NaCl-3CaAl2Si2O8-(CaCO3, CaSO4). The end sodium member of the series is called maria-lite, and the end calcium member, meionite. The intermediate members of the series include dipyre (20–50 percent of the meionite component) and mizzonite (50–80 percent).

Structurally, scapolite consists of a framework of quaternary ring-shaped groups of aluminosilicate tetrahedrons. Na+ and Ca2+ ions are housed in the smaller vacancies, and ClScapolite, and Scapolite anions are accommodated in the larger ones. Scapolites form either acicular crystals of the tetragonal system or solid granular aggregates. They have a hardness on Mohs’ scale of 5–6, and the density is 2,500–2,780 kg/m3. Colors are white, yellow, blue (glaucolite), or pink.

Scapolites are widespread in calcium-rich metamorphic rocks (marbles, gneisses, granulites, greenschist), skarns, and hydrothermally altered (through plagioclase minerals) basic magmatic rocks. Large scapolite crystals are found in the USSR in the Baikal Region (Sliudianka and Malaia Bystraia rivers) and in the Il’men Mountains in the Urals. They are also found in Finland, Norway, Madagascar, and Canada. Scapolites are used as industrial stones (glaucolite). Kaolins are formed through the weathering of scapolites.

A. S. MARFUNIN

References in periodicals archive ?
The rock contains aggregates optically resembling whitish scapolite or marialite, but dravite crystals potentially occurring together with marialite were not found in the material.
He is proud of the miniature to small cabinet-size pieces of typical (for the area) white marble matrix from which rise totally gemmy, pale lavender, well terminated prismatic crystals of scapolite to 4 cm long, with some of the same matrix pieces also bearing rounded, translucent pine-green diopside crystals, also to 4 cm.
The researchers suggest that one possible source of scapolite on Mars could have been carbon dioxide combined with calcium plagioclase, probably produced by volcanoes in the ancient Martian past.
Other gem mineral deposits include the Mpwapwa district in the Dodoma region (for yellow scapolite crystals), Babati in the Manyara region (dichroic cordierite), the Sumbawanga and Lake Manyara deposits (emerald and alexandrite), the sapphire, tourmaline and alexandrite deposits of Songea and Tunduru in the Ruvuma region, the Williamson (Mwadui) diamond deposit (the world's largest exploitable kimberlite pipe) in the Tabora region, the Umba River deposit in the Tanga region (sapphire, "umbalite" variety of almandine, and chromium-rich elbaite), Sangasanga in the Morogoro region (liddicoatite and rossmanite), and the Ipanko mines near Mahenge (big red spinel crystals)-among others.
Tucson 2015: exceptional colored stones and gem artistry, Brazilian Cu-bearing tourmaline and emerald, Oregon sunstone and pearl market updates * Conference reports * Amblygonitemontebrasite carving * Moroccan amethyst * Dumortierite in quartz * Jadeite with high albite content * Moldavite imitation * Iridescent scapolite * Composite quartz beads * CVD synthetic diamond with unstable color * The Foldscope.
Beds of massive, coarse-grained crystalline limestone, commonly dolomitic and siliceous, are prominent; MacFarlane (1975) found ubiquitous dispersed flakes of phlogopite and graphite in the limestone, along with lesser amounts of apatite, scapolite, tremolite, diopside, forsterite, hornblende and garnet.
The locality is Mpwapwa, Dodoma Province, to which are attributed also those lovely yellow gem scapolite crystals which we've been seeing around for years.
Meanwhile, in his Mineral Zone warehouse on North Main Street (mentioned earlier), Marcus Origlieri offered about 20 loose, fat, medium-purple, partially gemmy crystals of meionite (the most common of the three members of the scapolite group), from Badakhshan.
Transparent to milky, prismatic, lustrous scapolite crystals to more than 2 cm have been found at Alchuri, some in clusters to more than 6 cm.
They occur with clinopyroxene, mica, plagioclase, scapolite, nepheline and calcite; petrographic studies suggest that these minerals record a diverse, largely retrograde, progression of assemblages.
In that same report, the scapolite displayed at the Show and shown in Figure 24 is from the Gene and Roz Meieran collection, not the Bill Larson collection.
The Tucson Show of 2004 saw a tentative trickle of lustrous, gemmy, pale purple crystals of scapolite (to which species of the scapolite group the material belongs is so far undetermined) from the Kokcha Valley, Badakhshan, Afghanistan; some labels further specify that the locality is near the village of Kiran.