Leadhillite is a lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 sulfate

Sulfate

In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...

 carbonate

Carbonate

In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

 hydroxide

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 mineral, often associated with anglesite

Anglesite

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...

. It has the formula Pb₄SO₄(CO₃)₂(OH)₂.
Leadhillite crystallizes in the monoclinic system, but forms pseudo-hexagonal forms due to crystal twinning

Crystal twinning

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....

. It forms transparent to translucent variably colored adamantine crystals. It is quite soft with a Mohs hardness of 2.5 and a relatively high specific gravity of 6.26 to 6.55.

It was discovered in 1832 in the Susannah Mine, Leadhills

Leadhills

Leadhills is a village in South Lanarkshire, Scotland, 5¾ miles WSW of Elvanfoot. Population 835. Originally known as Waterhead, It is the second highest village in Scotland after Wanlockhead, lying 395m above sea-level, near the source of Glengonnar Water, an affluent of the River Clyde...

 in the county of Lanark

Lanark

Lanark is a small town in the central belt of Scotland. Its population of 8,253 makes it the 100th largest settlement in Scotland. The name is believed to come from the Cumbric Lanerc meaning "clear space, glade"....

, Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

.