Anglesite

Anglesite
Anglesite from Touizit, Morocco
General
Category	Sulfate minerals
Formula (repeating unit)	PbSO4
Strunz classification	7.AD.35
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Identification
Color	Colorless to white, commonly tinted gray; orange, yellow, green, blue, rarely violet
Crystal habit	Granular, banded, nodular to stalactitic
Cleavage	[001] good, [210] distinct
Fracture	Brittle to conchoidal
Mohs scale hardness	2.5–3.0
Luster	Adamantine crystals, dull when massive earthy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	6.3
Optical properties	Biaxial (+)
Refractive index	nα = 1.878 nβ = 1.883 nγ = 1.895
Fusibility	1.5
References

Anglesite is a lead sulfate mineral with the chemical formula PbSO₄. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and celestine. It contains 74% of lead by mass and therefore has a high specific gravity of 6.3. Anglesite's color is white or gray with pale yellow streaks. It may be dark gray if impure.

It was first recognized as a mineral species by William Withering in 1783, who discovered it in the Parys copper-mine in Anglesey; the name anglesite, from this locality, was given by F. S. Beudant in 1832. The crystals from Anglesey, which were formerly found abundantly on a matrix of dull limonite, are small in size and simple in form, being usually bounded by four faces of a prism and four faces of a dome; they are brownish-yellow in colour owing to a stain of limonite. Crystals from some other localities, notably from Monteponi () in Sardinia, are transparent and colourless, possessed of a brilliant adamantine lustre, and usually modified by numerous bright faces. The variety of combinations and habits presented by the crystals is very extensive, nearly two hundred distinct forms being figured by V. von Lang in his monograph of the species; without measurement of the angles the crystals are frequently difficult to decipher. There are distinct cleavages parallel to the faces of the prism (110) and the basal plane (001), but these are not so well developed as in the isomorphous minerals barite and celestite.

Anglesite is a mineral of secondary origin, having been formed by the oxidation of galena in the upper parts of mineral lodes where these have been affected by weathering processes. At Monteponi the crystals encrust cavities in glistening granular galena; and from Leadhills, in Scotland, pseudomorphs of anglesite after galena are known. At most localities it is found as isolated crystals in the lead-bearing lodes, but at some places, in Australia and Mexico, it occurs as large masses, and is then mined as an ore of lead.