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.
However, a number of papers have solved various aspects of the metasomatic processes including widespread formation of scapolite metagabbro [19-21, 27] through Mg-Cl metasomatism, replacement textures in apatite [28-30], rutile formation [31], carbonate deposition [32], tourmaline formation [33], and sapphirine-corundum crystallization [34].
Milisenda (German Gemmological Association, IdarOberstein) and co-authors examined some gemstones with photochromism: hackmanite, tugtupite and scapolite. The interesting colour behaviour of these gems is due to S- ions.
Somewhere near Karur, Tamil Nadu State, southern India, at least three impressive specimens of scapolite have recently come to light.
Pseudomorphs of muscovite: Gigantolite (after cordierite), Cataspilite (after cordierite), Pinite (after cordierite); Oncophyllite (after feldspars), Pinitoide (after feldspars); Gieseckite (after nepheline), Liebenerite (after nepheline); Gilbertite (after topas); Killinite (after spodumen); Terenite (after scapolite), Wilsonite (after scapolite).
A combination of well-characterized minerals and synthetic materials were used to calibrate for EPMA, including SMS scapolite (S and Cl), Corning W glass (6) (Co), SMS gahnite (Zn), SMS cassiterite (Sn), SMS strontianite and Corning X glass (Sr).
Called scapolite, it is somewhat rare on Earth, where it usually forms by heat-processing of carbonate rocks, often at points of contact with volcanic rocks.
Diamond-bearing eclogite xenoliths * Cat's-eye calcite from Pakistan * Large chatoyant Brazilian emerald * Nonbeadcultured pearls from Strombus gigas * Purple scapolite * Synthetic star sapphire with diffusion-induced colour and star * Partially filled blue chalcedony * Presumably oiled ruby * Inclusions in synthetic star sapphire * Diamond slices * Large Namibian demantoid * Nephrite from British Columbia * Baroque cultured pearls * Ruby from Namya, Myanmar * Rock Creek sapphire update * Unusual tourmaline necklace * Conference reports.
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.
Formation of inorganic, non-volatile chlorine compounds such as NaCl, KCl, Ca[Cl.sub.2], complex silicates and alumino-silicates like sodalite [Na.sub.8][[(AlSi[O.sub.4]).sub.6][Cl.sub.2]] or scapolite [(Na,Ca).sub.4][[Al.sub.3][(Si,Al).sub.3][Si.sub.6][O.sub.24](Cl,C[O.sub.3])] is of decisive importance.
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.