PYROMORPHITE  , a

mineral species composed of lead chloro- Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid . Crystals with a 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 apatite, with which mineral pyromorphite and also mimetite are isomorphous . Between pyromorphite and the corresponding chloro-arsenate (mimetite, (q.v.) the resemblance in external characters is so close that, as a rule, it is only possible to distinguish between them by chemical tests: and they were formerly confused under the names " green lead ore " and " brown lead ore " (German, Griinbleierz and Braunbleierz) . The phosphate was first distinguished chemically by M . H . Klaproth, in 1784, and it was named pyromorphite by J . F . L . Hausmann in 1813, being so named from the Gr. xup (fire) and uopcpn (form), because when a fragment of the mineral is fused the globule assumes a faceted form on solidifying . The colour of the mineral is usually some 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

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