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K2(Li,Fe,Al)6(Si,Al)8O20(OH,F)4 A pale-violet, yellowish, brown, or dark-gray mica mineral; an iron-bearing variety of lepidolite; the characteristic mica of greisens.
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 It might be outdated or ideologically biased.



(after the deposit at Zinnwald, now Cínovec, Czechoslovak Socialist Republic), a mineral; a phyllosilicate belonging to the mica group. Its chemical composition is KLiFe2+ Al [AlSi3O10](OH, F)2. Zinnwaldite is an intermediate member of the biotite-lepidolite isomorphic series. Typical impurities are Rb2O (up to 1 percent), Cs2O (up to 0.2 percent), Ga, and Sc. The amount of fluorine ranges from 2.5 to 5.0 percent. Zinnwaldite crystallizes in the monoclinic system, forming small pseudohexagonal plates, blades, and tabular colloform crystals with clearly expressed zonal structure. Colors range from dark green to brown. The physical properties of zinnwaldite are similar to those of other micas. The density is 2,990 kg/m3.

Zinnwaldite is found in the cavities of granitic pegmatites and lithium fluoride-type tantalum-bearing granites, in which zinnwaldite develops after biotite and protolithionite. It is also found in tin-tungsten greisen and quartz-vein formations. It is associated with topaz. Where significant quantities of zinnwaldite occur as a by-product, they may serve as an ore of lithium and rubidium.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Just 15 km to the south-east, silvery brown zinnwaldite in bladed spheres exceeding 5 cm is particularly common in the quarry pegmatite, one of many in the Cocanarup pegmatite field.
Zinnwaldite Kli[Fe.sup.2+]Al(Al[Si.sub.3])[O.sub.10](F,OH)[.sub.2]
There is some confusion regarding the existence of zinnwaldite in the Erongo miarolitic cavities and surrounding pegmatites.
Zinnwaldite (see also lepidolite) KLi[Fe.sup.2+]Al(Al[Si.sub.3])[O.sub.10][(F,OH).sub.2]
Pale brown zinnwaldite occurs in miarolitic cavities with smoky quartz and amazonite.
Arsenic Arsenopyrite (*)Augelite Bornite Chalcopyrite Enargite (*)Fluorapatite Molybdenite (*)Scheelite Stolzite Topaz Tungstite (*)Vivianite Zinnwaldite
The locality is known for samarskite and a variety of other interesting species such as fayalite, gadolinite, zinnwaldite, bastnaesite, synchisite and xenotime.
As we know by now, some of these specimens can be very fine, with near-gemmy orange scheelite pseudo-octahedrons to several centimeters, gemmy flat beryls, and brilliant cassiterite clusters, all resting (though never all three on the same matrix) on flat plates of densely packed gray-white mica (zinnwaldite?) books lying edge-on.