Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb<sub>4</sub>SO<sub>4</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub>. 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

thumb|upright|left|alt=text|Blue leadhillite from the [[Mammoth, Arizona|Mammoth-Saint Anthony Mine, Arizona, USA]]

thumb|upright|left|alt=text|Pale grey-blue leadhillite from [[Tsumeb]]

thumb|upright|left|alt=text|Leadhillite from the Beer Cellar Mine, [[Missouri, USA]]

Structure

Leadhillite has a layered structure. The mineral contains both carbonate and sulfate groups, and these are arranged in separate sheets. Pairs of carbonate sheets 8(PbCO<sub>3</sub>) alternate with pairs of sulfate sheets 8[Pb(SO<sub>4</sub>)<sub>0.5</sub>OH]. The carbonate sheets virtually have trigonal symmetry, but the sulfate sheets do not. All the lead (Pb) atoms in the carbonate sheets are surrounded by 9 oxygens from carbonate groups and by one hydroxyl from an adjacent sulfate sheet. The Pb atoms in the sulfate sheets are bonded to 9 or 10 oxygens. <br />

Leadhillite is soluble with effervescence in nitric acid HNO<sub>3</sub>, leaving lead sulfate.