Susannite

Susannite is a lead sulfate carbonate hydroxide mineral. It has the formula Pb₄SO₄(CO₃)₂(OH)₂. Susannite is the higher temperature phase of the two and forms above 80 °C when fluids oxidize the lead ore deposits. It is trimorphous with leadhillite and macphersonite.[3]

Susannite
Susanite with macphersonite and lanarkite from the Susanna Mine, Leadhills
General
Category	Carbonate minerals
Formula (repeating unit)	Pb4SO4(CO3)2(OH)2
Strunz classification	5.BF.40
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H-M symbol: (3)
Space group	R3
Unit cell	a = 9.07, c = 11.57 [Å]; Z = 3
Identification
Color	Colorless, white, pale green, pale yellow, brown
Crystal habit	Occurs as equant to acute rhombohedral crystals
Cleavage	{0001} perfect
Mohs scale hardness	2.5 - 3
Luster	Adamantine, resinous
Diaphaneity	Translucent
Specific gravity	6.55
Optical properties	Uniaxial (anomalously biaxial)
Refractive index	1.96
References	[1][2][3]

Susannite crystallizes in the trigonal system. It is quite soft with a Mohs hardness of 2.5 to 3.0 and a relatively high specific gravity of 6.57.

An old beam engine to dewater a lead mine at nearby Wanlockhead

It was discovered in 1827 in the Susannah Mine, Leadhills in the county of Lanark, Scotland.[2] In addition to the type locality in Scotland, it has also been reported from various locations in Germany, the Tiger Mine in Pinal County, Arizona, from Iporanga, Sao Paulo, Brazil, and the Tsumeb mine of Namibia.[3]