Phlogopite

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phlogopite

[′fläg·ə‚pīt]
(mineralogy)
K2[Mg,Fe(II)]6(Si6,Al2)O20(OH)4 A yellow-brown to copper mineral of the mica group occurring in disseminated flakes, foliated masses, or large crystals; hardness is 2.5-3.0 on Mohs scale, and specific gravity is 2.8-3.0. Also known as bronze mica; brown mica.

Phlogopite

 

a mineral of the phyllosilicate class; an iron-poor magnesium mica (Mg/Fe > 2) of the isomorphic biotite-phlogo-pite series. Phlogopite has a chemical composition of K(Mg, Fe)3[AlSi3O10](OH, F)2. Impurities include Na2O (up to 8 percent), TiO2 (up to 9 percent), and MnO (up to 18 percent; such phlogopite is called manganophyllite), as well as rubidium, cesium, and barium. In man-made fluorphlogopite, all the (OH) is substituted by fluorite.

Phlogopite crystallizes in the monoclinic system, forming pseu-dohexagonal tabular, prismatic, or other types of crystals, which reach 2 m in length; it also forms foliated or scaly aggregates. Iron-free phlogopites are colorless, while ferruginous phlogopites are green and brown and have a characteristic reddish tint. Phlogopite has perfect cleavage and splits easily into flexible sheets. It has a hardness of 2–2.5 on Mohs’ scale and a density of 2,700–2,850 kg/m3. It is a good dielectric.

Phlogopite is widely distributed in metamorphic rocks and upon weathering alters to vermiculite. Industrially useful deposits occur as a result of metasomatism at the contact zone of magnesium rocks (dolomites, hyperbasic rocks) and aluminosilicate rocks (gneisses, pegmatites, alkali magmatites).

Because of its excellent electrical insulating properties, phlogopite is used in electrical technology. In this case, the value of the raw material is determined by the size of defect-free crystals. Phlogopite is partially replaced by synthetic fluorphlogopite, crystallized from a melt.

The USSR has the largest phlogopite province in the world at Aldan (the Emel’dzhak, Timpton, Kuranakh, and other deposits), as well as deposits on the Kola Peninsula (Kovdor and others), in the Transbaikal Region (Sliudianka), and elsewhere. Phlogopite is also found on Madagascar and in Canada, Sri Lanka, India, and North Korea.

REFERENCES

Litsarev, M. A. Genezis flogopitovykh mestorozhdenii Aldana. Moscow, 1961.
Ternovoi, V. I., B. V. Afanas’ev, and B. I. Sulimov. “Geologicheskoe stroenie i usloviia obrazovaniia Kovdorskogo mestorozhde-niia flogopita.” Sovetskaia geologiia, 1967, no. 2.

P. P. SMOLIN