Langite is a rare hydrated copper

sulfate mineral The sulfate minerals are a class of minerals that include the sulfate ion () within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal Vein (geology), veins and as ...

, with hydroxyl, found almost exclusively in druses of small crystals. It is formed from the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

copper sulfide Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores. Prominent copper sulfide minerals ...

s, and was first described in specimens from

Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...

, United Kingdom. It is dimorphous with wroewolfeite. Langite was discovered in 1864 and named after the physicist and crystallographer Viktor von Lang (1838–1921), who was Professor of Physics at the

University of Vienna The University of Vienna (, ) is a public university, public research university in Vienna, Austria. Founded by Rudolf IV, Duke of Austria, Duke Rudolph IV in 1365, it is the oldest university in the German-speaking world and among the largest ...

, Austria.

Unit cell

Langite belongs to the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

crystal class m, meaning that it has just one mirror plane, and no axes of rotational symmetry. The crystal is built up of identical unit cells stacked together, with no space in between. The unit cell for the monoclinic system has a base which is a

rhombus In plane Euclidean geometry, a rhombus (: rhombi or rhombuses) is a quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The rhom ...

, with sides a and c inclined at angle β. The third side b is perpendicular to both a and c. For langite the angle β is very close to 90°, so the unit cell is almost brick-shaped (as for the

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

system). Different sources give slightly different values for the unit cell parameters, but they all fall within the ranges a = 7.118 Å to 7.137 Å, b = 6.031 Å to 6.034 Å, c = 11.209 Å to 11.217 Å, β = 90.00 to 90.02°, Z (the number of formula units per unit cell) = 2.

Physical properties

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 Cleavage may refer to: Science * Cleavage (crystal), the way in which a crystal or mineral tends to split * Cleavage (embryo), the division of cells in an early embryo * Cleavage (geology), foliation of rock perpendicular to stress, a result of ...

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 In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

2.5 to 3, a little less than that of calcite.

Fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

is uneven, and

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

is in the range 3.28 to 3.50, a little less than that of diamond.

Optical properties

Langite is biaxial (−). Since it is monoclinic, it has three different refractive indices, corresponding to the three crystallographic directions. All the refractive indices are in the range 1.64 to 1.80, which is comparatively large, almost as high as garnet. Different sources give these values: :N_x = 1.641, N_y = 1.690, N_z = 1.712 :N_x = 1.708, N_y = 1.760, N_z = 1.798 :N_x = 1.641 to 1.654, N_y = 1.690 to 1.713, N_z = 1.705 to 1.722 :N_x = 1.641, N_y = 1.690, N_z = 1.705 to 1.712American Mineralogist (1964) 49:1143 The mineral is

pleochroic Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Etymology The roots of the word are from Greek (). It was first made compound in the German term ...

, with X light yellowish green, Y blue-green and Z sky blue.

Occurrence

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 Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is Cu4SO4(OH)6. Formed in arid climates or in rapidly oxidizing copper sulfide deposits, it was named by Armand Lévy (mineralogist), Armand Lévy for his ...

malachite Malachite () is a copper Carbonate mineral, carbonate hydroxide mineral, with the chemical formula, formula Basic copper carbonate, Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often for ...

and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

. There are two type localities for langite, Fowey Consols,

Tywardreath Tywardreath (; , meaning "House on the Beach" (or Strand)) is a small hilltop village on the south coast of Cornwall, England, United Kingdom, about north west of Fowey. It is located in a sheltered spot overlooking a silted-up estuary opposite ...

, Par Area,

St Austell Saint Austell (, ; ) is a town in Cornwall, England, United Kingdom, south of Bodmin and west of the border with Devon. At the 2021 Census in the United Kingdom, census it had a population of 20,900. History St Austell was a village centred ...

District, and St Just, St Just District, both in Cornwall, England. The type material is conserved at the

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history scientific collection, collections that include current and historical records of animals, plants, Fungus, fungi, ecosystems, geology, paleo ...

, Vienna, Austria, reference A.a.4353. Other reported occurrences include: * With serpierite coating the bed of a water course affected by

acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines and coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weatherin ...

at the Lloyd Copper Mine at Burraga, New South Wales, AustraliaAustralian Journal of Mineralogy (2004) 10-1:3 * 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 Broken Hill is a city in the Far West (New South Wales), far west region of outback New South Wales, Australia. An inland mining city, it is near the border with South Australia on the crossing of the Barrier Highway (A32) and the Silver City Hi ...

, AustraliaAustralian Journal of Mineralogy (1997) 3-1:43 * Associated with a new mineral mallestigite, reported in 2004, near

Carinthia Carinthia ( ; ; ) is the southernmost and least densely populated States of Austria, Austrian state, in the Eastern Alps, and is noted for its mountains and lakes. The Lake Wolayer is a mountain lake on the Carinthian side of the Carnic Main ...

, Austria, on the dump of a copper-lead-zinc mine. The mallestigite formed in fractures during weathering of primary

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...

and

tetrahedrite Tetrahedrite is a copper antimony sulfosalt mineral with formula: . It is the antimony endmember of the continuous solid solution series with arsenic-bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, ...

. Other associated minerals were

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 ...

linarite Linarite is a somewhat rare, crystalline mineral that is known among mineral collectors for its unusually intense, pure blue color. It is formed by the oxidation of galena and chalcopyrite and other copper sulfides. It is a combined copper lead s ...

and schulteniteThe Mineralogical Record (2004) 35-4:357 * At Silver Gill, Caldbeck Fells,

Cumbria Cumbria ( ) is a ceremonial county in North West England. It borders the Scottish council areas of Dumfries and Galloway and Scottish Borders to the north, Northumberland and County Durham to the east, North Yorkshire to the south-east, Lancash ...

, England, partly altered to

, Cu₄SO₄(OH)₆Mines & Minerals (2005)25:6 * As microcrystals in small vugs in

prehnite Prehnite is an inosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2 with limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, and most often forms as stalactitic ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

vein sections at the Clark Mine,

Keweenaw Peninsula The Keweenaw Peninsula (, ) is a peninsula of the U.S. state of Michigan. Part of the greater landmass of the Upper Peninsula of Michigan, Upper Peninsula, the Keweenaw Peninsula projects about northeasterly into Lake Superior, forming Keweena ...

, Michigan, USRocks & Minerals (2009) 84-4:321

References

External links

*Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=09777 {{Authority control Copper(II) minerals Sulfate minerals Monoclinic minerals Minerals in space group 7