leadhillite

{{Infobox mineral | name = Leadhillite | boxwidth = | boxbgcolor = | image = Leadhillite-189253.jpg | imagesize = 200px | alt = | caption = Thin crystals of transparent leadhillite, inside a vug of galena which seems to be partially altered to cerussite. From the type locality, Leadhills, South Lanarkshire, Scotland. Size: 5.3 x 5.1 x 4.4 cm. | category = Carbonate minerals | formula = Pb4SO4(CO3)2(OH)2 | IMAsymbol = Lhl | molweight = 1,078.90 g/mol | strunz = 5.BF.40 | dana = 17.1.2.1 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/a | unit cell = a = 9.11, b = 20.82 c = 11.59 [Å]; β = 90.46°; Z = 8 | color = | colour = Colourless to white, grey, yellowish, pale green to blue | habit = Usually pseudo-hexagonal, thin to thick tabular {001} with hexagonal outline | twinning = Commonly twinned, twin plane {140} | cleavage = Perfect on {001} | fracture = Irregular to conchoidal | tenacity = sectile | mohs = to 3 | lustre = Adamantine, resinous, pearly | streak = White | diaphaneity = Transparent to translucent | gravity = 6.55 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.87, nβ = 2.00, nγ = 2.01 | birefringence = 0.140 | pleochroism = | 2V = 10° | dispersion = Strong, r3 | impurities = | alteration = Galena, calcite and susannite may alter to leadhillite. Leadhillite may alter to cerussite, calcite and susannite | other = Not radioactive | prop1 = | prop1text = | references = }}

Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb4SO4(CO3)2(OH)2. Leadhillite crystallises in the monoclinic system, but develops pseudo-hexagonal forms due to crystal twinning. It forms transparent to translucent variably coloured crystals with an adamantine lustre. It is quite soft with a Mohs hardness of 2.5 and a relatively high specific gravity of 6.26 to 6.55.