Sillimanite


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sillimanite

[′sil·ə·mə‚nīt]
(mineralogy)
Al2SiO5 A brown, pale-green, or white neosilicate mineral with vitreous luster crystallizing in the orthorhombic system; commonly occurs in slender crystals, often in fibrous aggregates; hardness is 6-7 on Mohs scale, and specific gravity is 3.23. Also known as fibrolite.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sillimanite

 

a mineral of the silicate class. Sillimanite is a high-temperature, polymorphic modification of the composition Al[AlSiO5] and contains 1–1.5 percent Fe2O3 in admixture form. The sillimanite structure is made up of chains of alternating SiO4 and AlO4 tetrahedrons, connected by chains of Al octahedrons. The mineral crystallizes in the orthorhombic system, forming acicular crystals, compact radiated masses, or thin fibrous aggregates. It sometimes forms dispersed, filiform inclusions in other minerals (fibrolite variety). Sillimanite is gray, light brown, or pale green; it has a vitreous luster, a hardness of 6.5-7.5 on Mohs’ scale, and a density of 3,270 kg/m3. At high temperatures (approximately 1545°C), it decomposes into mullite and silica.

Sillimanite occurs in thermally and regionally metamorphosed clay rocks. It serves as a raw material in the production of refractories and acid-resistant products with a high alumina content. The largest known sillimanite deposits are in India (Khasi Hills and Pipri).

REFERENCE

Kostov, 1. Mineralogiia. Moscow, 1971. (Translated from English.)
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Sample Principal Secondary Trace (<5%) phase (>50%) phase (10-40%) Huayacocotla H-RMC-4 An Kln -- H-RMC-9 Cr Kln Mag H-RMC-14 Cr Kln Qz H-RMC-21 An Kln Mag H-RMC-32 An Qz -- H-RMC-35 Kln Qz -- Alumbres A-RMC-25 Qz Py Ill A-RMC-26 Qz Py Kln, Ill A-RMC-40 An Dck Cr, Ill, Sil A-RMC-45 An Dck Qz, An = andalusite, Cr = cristobalite, Qz = quartz, Kln = kaolinite, Dck = dickite, Py = pyrite, Mag = magnetite, 1ll = illite, Sil = sillimanite. Table 5: Pearson correlation of kaolin from Huayacocotla Ver.
Caption: Figure 4: Mineralogy of expansive soil and stabilized soil by (a) raw PG (M: montmorillonite; B: bentonite; Q: quartz; G: gypsum; K: kaolinite; F: feldspar) and (b) treated PG (M: montmorillonite; B: bentonite; Q: quartz; G: gypsum; K: kaolinite; F: feldspar; TK: trikalsilite; CMS: calcium magnesium silicide; S: sillimanite).
After the purification process the chemical composition of the bulk clay changed due to the presence of clay minerals like quartz, feldspar, sillimanite, plagioclase, and cristobalite which were removed from the sample (Figure 3), meaning changes in the chemical composition as shown in Table 2.
From the whole story of polymetamorphism it seems that kyanite belongs to the early events with deformation and andalusite and sillimanite (fibrolite) to the late (contact) metamorphism.
The accessory minerals included zircon, apatite, ilmenite, sillimanite and monazite, while muscovite, chlorite, anatase, sericite and pinite were identified as the secondary minerals.
Petrographic study indicates the occurrence of microcrystalline polycrystalline micro-fractured strained and angular quartz grains plus the sillimanite protrusion in quartz make the aggregate samples extremely vulnerable to deleterious ASR.
The common impurities in bauxite are hematitie goethite titania lipidocrosite kaolinite pyrophyllite illite quartz sillimanite corundum rutile garnet vanadium etc.
Jharkhand is known for its rich store of minerals, like coal, iron ore, copper ore, bauxite, mica, graphite, kyanite, sillimanite and limestone, and it forms an integral part of the economy of Jharkhand.
Newman provides identification, evaluation/pricing, and care information on rarely heard of gems (e.g., andulusite, kyanite, sillimanite); ones often sold in rock and mineral stores (agatized dinosaur bone and coprolites); and "common" opals that are anything but, as color photos of loose and mounted gems show.
When sillimanite (later designated the official mineral of the state of Delaware) was incorporated into porcelain formulas, the result was the long-lasting plug.
The major lithostratigraphic units in the study area include garnet bearing charnockitic, garnet rich and sillimanite rich metapellataic geneisses (khondalitic) and garnet biotite quartz feldspar gneisses underlain by black cotton soil Chetty Q996),Braun et.al (1998), Shabeer et.al (2005)
Rock-forming minerals such as kyanite, vanadian phlogopite, fuchsite, quartz, sillimanite, and tourmaline group species occur in the vein rock.