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PYROMORPHITE

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Originally appearing in Volume V22, Page 694 of the 1911 Encyclopedia Britannica.
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PYROMORPHITE , a See also:

mineral See also:species composed of See also:lead chloro- Crystals are See also:common, and have the See also:form of a hexagonal See also:prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal See also:pyramid. Crystals with a See also:barrel-like curvature are not uncommon. Globular and reniform masses are also found. As proved by the etched figures on the faces, crystals possess the same parallel-faced hemihedrism as See also:apatite, with which mineral pyromorphite and also See also:mimetite are isomorphous. Between pyromorphite and the corresponding chloro-arsenate (mimetite, (q.v.) the resemblance in See also:external characters is so See also:close that, as a See also:rule, it is only possible to distinguish between them by chemical tests: and they were formerly confused under the names " See also:green lead ore " and " See also:brown lead ore " (See also:German, Griinbleierz and Braunbleierz). The phosphate was first distinguished chemically by M. H. See also:Klaproth, in 1784, and it was named pyromorphite by J. F. L. See also:Hausmann in 1813, being so named from the Gr. xup (See also:fire) and uopcpn (form), because when a fragment of the mineral is fused the globule assumes a faceted form on solidifying. The See also:colour of the mineral is usually some See also:bright shade of green, yellow or brown, and the lustre is resinous.

The hardness is 3 and the specific gravity 6.5–7.1. Owing to isomorphous replacement of the See also:

phosphorus by See also:arsenic there may be a ‘.See also:gradual passage from pyromorphite to mimetite. Varieties containing See also:calcium isomorphously replacing lead are See also:lower in .See also:density' (specific gravity 5.9–6.5) and usually lighter in colour; they See also:bear the names " polysphaerite " (because of the globular fotm),'°` miesite " from Mies in Bohemia, " nussierite from Nu8sihre near See also:Beaujeu, See also:Rhone, See also:France, and " cherokine" from See also:Cherokee See also:county in See also:Georgia. 694 Pyromorphite has resulted from the alteration of See also:galena in the oxidized portions of metalliferous See also:veins, and is frequently met with in the upper levels of lead mines. Finely crystallized specimens have been found at Braubach and See also:Ems in See also:Nassau, Wheal See also:Alfred in See also:Cornwall, Roughten Gill in See also:Cumberland, See also:Leadhills in See also:Scotland, See also:Phoenixville in See also:Pennsylvania, Huelgoat in See also:Finistere, See also:Brittany, &c. At the last-named locality, as well as at Wheal See also:Hope, near See also:Truro in Cornwall, there were formerly found curious pseudomorphs of galena after pyromorphite, known as " See also:blue lead ore." (L. J.

End of Article: PYROMORPHITE

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