LEADHILLITE

This article appears in Volume V16, Page 320 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: LAP-LEO

LEADHILLITE , a rare

mineral

MINERAL

consisting of basic lead sulphatocarbonate, Pb4 SO4 (CO3)2(OH)2. Crystals have usually the 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 white and translucent. The hardness is 2.5 and the sp. gr. 6.26-6.44. The crystallographic and optical characters point to the existence of three distinct kinds of leadhillite, which are, however, identical in external

appearance

APPEARANCE (from Lat. apparere, to appear)

and may even occur intergrown together in the same crystal: (a) monoclinic with an optic axial

angle

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form,
angus
- ANGUS, EARLS OF
, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

of 200; (b) rhombohedral (fig. 2) and optically
uniaxial; (c) orthorhombic (fig. I) with an optic axial

angle

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form,
angus
- ANGUS, EARLS OF
, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

of 721. The first of these is the more common kind, and the
second has

long

LONG, GEORGE (1800-1879)
LONG, JOHN DAVIS (1838– )

been known under the name susannite. Tits fact that the published analyses of leadhillite vary somewhat from the

formula

given above suggests that these three kinds may also be chemically distinct.
Leadhillite is a

mineral

MINERAL

of secondary origin, occurring with cerussite, anglesite, &c., in the oxidized portions of lead-bearing lodes; it has also been found in weathered lead slags left by the Romans. It has been found most abundantly in the Susanna mine at Leadhills in

Scotland

(hence the names leadhillite and susannite). Good crystals have also been found at Red Gill in

Cumberland

and at Granby in Missouri. Crystals from Sardinia have been called maxite. (L. J. S.)

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