Chamosite


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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.

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

References in periodicals archive ?
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).
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.
Calcite-I, which was the first mineral to crystallize (with the exception of a thin layer of chamosite which often coats the vein walls), forms rhombohedral crystals, usually twinned on {00011}.
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.
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.