Langite

Langite usually occurs as druses of small greenish-blue crystals which may be scaly or earthy. It is translucent, with a vitreous to silky luster and a blue-green streak. It has perfect cleavage perpendicular to the c crystal axis, and distinct cleavage perpendicular to b. Twinning is common, and typically repeated to give snowflake or star shaped groupings. The mineral is soft, with hardness 2.5 to 3, a little less than that of calcite. Fracture is uneven, and specific gravity is in the range 3.28 to 3.50, a little less than that of diamond.

Langite is an uncommon but widespread secondary mineral in the oxidised zone of copper sulfide deposits, which may be of post-mine formation. It is associated with wroewolfeite, posnjakite, serpierite, devilline, chalcophyllite, connellite, brochantite, malachite and gypsum. There are two type localities for langite, Fowey Consols, Tywardreath, Par Area, St Austell District, and St Just, St Just District, both in Cornwall, England. The type material is conserved at the Natural History Museum, Vienna, Austria, reference A.a.4353. Other reported occurrences include: With serpierite coating the bed of a water course affected by acid mine drainage at the Lloyd Copper Mine at Burraga, New South Wales, Australia Intergrown with ktenasite forming fibrous and botryoidal crusts and coatings less than 0.1 mm thick, at the Kintore Open Cut, Broken Hill, New South Wales, Australia Associated with a new mineral mallestigite, reported in 2004, near Carinthia, Austria, on the dump of a copper-lead-zinc mine. The mallestigite formed in fractures during weathering of primary galena and tetrahedrite. Other associated minerals were anglesite, brochantite, linarite and schultenite At Silver Gill, Caldbeck Fells, Cumbria, England, partly altered to brochantite, Cu4SO4(OH)6 As microcrystals in small vugs in prehnite-quartz vein sections at the Clark Mine, Keweenaw Peninsula, Michigan, US