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LEADHILLITE

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Originally appearing in Volume V16, Page 320 of the 1911 Encyclopedia Britannica.
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LEADHILLITE , a rare See also:

mineral consisting of basic See also:lead sulphatocarbonate, Pb4 SO4 (CO3)2(OH)2. Crystals have usually the See also:form of six-sided plates (fig. 1) or sometimes of acute rhombohedra (fig. 2); they have a perfect basal cleavage (parallel to P in fig. I) on which the lustre is strongly pearly; they are usually See also:white and translucent. The hardness is 2.5 and the sp. gr. 6.26-6.44. The crystallographic and See also:optical characters point to the existence of three distinct kinds of leadhillite, which are, however, identical in See also:external See also:appearance and may even occur intergrown together in the same crystal: (a) See also:monoclinic with an optic axial See also:angle of 200; (b) See also:rhombohedral (fig. 2) and optically uniaxial; (c) orthorhombic (fig. I) with an optic axial angle of 721°. The first of these is the more See also:common See also:kind, and the second has See also:long been known under the name susannite. Tits fact that the published analyses of leadhillite vary somewhat from the See also:formula given above suggests that these three kinds may also be chemically distinct.

Leadhillite is a mineral of secondary origin, occurring with See also:

cerussite, anglesite, &c., in the oxidized portions of lead-bearing lodes; it has also been found in weathered lead slags See also:left by the See also:Romans. It has been found most abundantly in the Susanna mine at See also:Leadhills in See also:Scotland (hence the names leadhillite and susannite). See also:Good crystals have also been found at Red Gill in See also:Cumberland and at See also:Granby in See also:Missouri. Crystals from See also:Sardinia have been called maxite. (L. J.

End of Article: LEADHILLITE

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