Chamosite


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Related to Chamosite: clinochlore

chamosite

[′sham·ə‚zīt]
(mineralogy)
A greenish-gray or black mineral consisting of silicate belonging to the chlorite group and having monoclinic crystals; found in many oolitic iron ores.
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 It might be outdated or ideologically biased.

Chamosite

 

(from the village of Chamoson in Switzerland). (1) A mineral of the subclass of phyllosilicates; an iron chlorite. Chamosite, whose chemical composition is (Fe, Al, Mg)3[(Si, Al)4O10](OH)2(Fe, Mg)3(O, OH)6, contains more than 30 percent iron oxides. The distance between layers in its structure is 14 angstroms.

(2) A mineral of the family of septechlorites; also known as berthierine or septechamosite. Its chemical composition is (Fe2+, Fe3+, Al, Mg)6[(Si, Al)4O10](OH)8. The mineral contains 40–45 percent iron oxides. The composition varies. The structure of chamosite resembles that of kaolinite; the distance between layers is 7 angstroms.

The two minerals may be found together and are difficult to distinguish. They crystallize in the monoclinic system (septechamosite also exhibits a hexagonal modification). They form green, yellow, or brown oolitic or fine-grained (to earthy) aggregates. The hardness on Mohs’ scale is 3, and the density varies from 3,000 to 3,300 kg/m3. Both are hypergenic in origin.

Chamosites are found in clay beds and sedimentary (oolitic) iron ores. Deposits in the USSR occur in the Urals (Alapaevsk, Aiat’, and Khalilovo). Other deposits are found in the Lorraine Basin in France, Northhamptonshire in Great Britain, Thuringia in East Germany, and Nucice in Czechoslovakia.

L. G. FEL’DMAN

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Origin of Constituting Minerals in Lithofacies of the Hangu Formation Lithofacies-I (laterite / bauxite / kaolinite): The petrographic results show that the principal clay minerals include kaolinite (50-65 (Percent) , boehmite (40-50 (Percent) , gibbsite (upto 30 (Percent) , neoformed clay (chamosite upto15 (Percent) and iron rich clay (glauconite 9-15 (Percent) alongwith nacrite / clinochlore (upto 85 (Percent) at Kalra Wahan) and chlorite (upto 5 (Percent) .
The presence of chamosite indicated near shore marine environment under weakly oxidizing to mildly reducing conditions, which was further supported by the dickite content of laterite exposed at Dhak Pass in the Western Salt Range (Wenk and Bulakh, 2008 and Greensmith, 1989).
Lithofacies-2 comprised of shale / clays, developed only in the Eastern Salt Range at Saloi (M-1/4-09) and Wehali Zirin (M-2/4-09) sites, had quartz (10 (Percent) and 20 (Percent) , kaolinite (60 (Percent) and 70 (Percent) , haematite / goethite (9 (Percent) and 11 (Percent) , chamosite (5 (Percent) and 6 (Percent) and muscovite flakes were (6 (Percent) only in the Saloi and around (3 (Percent) anatase was observed at Wehali Zirin.
The presence of glauconite (around 2-17 (Percent) and chamosite (about 2-5 (Percent) in the lithofacies-3 may reflect the near-shore marine depositional environment under oxidizing to mildly reducing conditions (Wenk and Bulakh, 2008; Baruah and Gogoi, 2004).
The allochthonous minerals (chamosite, glauconite, chlorite and nacrite / clinochlore) could be due to the influx of shallow marine water into the passive continental depositional basin.
* The subaerial emergence of the area was followed by subsidence, and the laterite / bauxite / kaolinite horizons were preserved by deposition of terrigenous material such as shales / clays (lithofacies-2).These shales / clays be formed in fresh water lagoon / estuary or delta front depositional basin, in which chamosite was formed under weakly oxidizing to mildy reducing conditions.
Typically, larger fluorite crystals are attached to the edges of calcite-I crystals, which in turn are attached to the vein walls or their initial chamosite coating.
Chamosite [([Fe.sup.2+],[Mg,[Fe.sup.3+]).sub.5]A1([Si.sub.3]A1)[O.sub.10][(OH,O ).sub.8]
Three generations of chamosite are present in the Long Lake veins.
Electron microprobe analyses of chamosite of the second and third (golden phase) generations yielded the following empirical formulae ([Fe.sup.2+], [Fe.sup.3+] and OH determined by stoichiometry):
On the sample which produced the majority of the specimens, titanite is definitely later in the paragenesis than chamosite, probably later than cerian epidote, definitely earlier than quartz, and of uncertain relationship to kainosite-(Y).