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 veins and as secondary mine ...

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

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

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 mineral ...

s, and was first described in specimens from

Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...

, 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 (german: Universität Wien) is a public research university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world. With its long and rich hist ...

, 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 vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

crystal class m, meaning that it has just one

mirror plane In mathematics, a reflection (also spelled reflexion) is a mapping from a Euclidean space to itself that is an isometry with a hyperplane as a set of fixed points; this set is called the axis (in dimension 2) or plane (in dimension 3) of ref ...

, 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 (plural 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 ...

, 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 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 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 localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

2.5 to 3, a little less than that of calcite. Fracture is uneven, and

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

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 (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgroun ...

, 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 Serpierite () is a rare, sky-blue coloured hydrated sulfate mineral, often found as a post-mining product. It is a member of the devilline group, which has members aldridgeite , campigliaite , devilline , kobyashevite , lautenthalite and an ...

devilline Devilline is a sulfate mineral with the chemical formula CaCu4(SO4)2(OH)6•3H2O. The name originates from the French chemist's name, Henri Etienne Sainte-Claire Deville (1818–1881). Devilline crystallizes in the monoclinic system. Crystallogr ...

chalcophyllite Chalcophyllite is a rare secondary copper arsenate mineral occurring in the oxidized zones of some arsenic-bearing copper deposits. It was first described from material collected in Germany. At one time chalcophyllite from Wheal Tamar in Cornwall ...

, 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 for his fellow Frenchman, geologist ...

malachite Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fracture ...

and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate 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, blackboard or sidewalk chalk, and drywal ...

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

Tywardreath Tywardreath (; kw, Ti War Dreth, 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 ...

, 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 A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

, Vienna, Austria, reference A.a.4353. Other reported occurrences include: * With

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 or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...

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, AustraliaAustralian Journal of Mineralogy (1997) 3-1:43 * 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 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 le ...

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

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. C ...

, England, partly altered to

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

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

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

vein sections at the Clark Mine, Keweenaw Peninsula, 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