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Plancheite is a hydrated
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...
silicate
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...
with the formula Cu8 Si8 O22( OH)4•( H2O). It is closely related to shattuckite in structure and appearance, and the two minerals are often confused.


Structure

Plancheite is a chain silicate (
inosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consi ...
), with double chains of silica
tetrahedra In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
parallel to the c crystal axis. It occurs as sprays of acicular or fibrous radial clusters, with fibers extended parallel to the chains, i.e. along the c crystal axis; it can also form tiny tabular or platy crystals. It is a member of the orthorhombic crystal class m m m (2/m 2/m 2/m), which is the most symmetrical class in the orthorhombic system.


Properties

Usually a pale turquoise-blue, with a pale blue streak and an adamantine to silky luster. It is quite hard, with hardness 5.5 to 6, close to that of feldspar, and specific gravity 3.6 to 3.8. Optically it is biaxial (+), with
refractive indices In optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of vi ...
between 1.64 and 1.74, and
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 ...
.


Environment

Plancheite is a secondary mineral formed in the
oxidized zone Gossan (eiserner hut or eisenhut) is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the ''classic'' gossan or iron cap all that remains is iron oxides and quartz, often i ...
of copper deposits, associated with other copper minerals
chrysocolla Chrysocolla ( ) is a hydrated copper phyllosilicate mineral and mineraloid with formula (x<1) or . The structure of the mineral has been questioned, as a 2006 spectrographic study suggest material identified ...
,
dioptase Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Its luster is vitreous to sub- adamantine. Its formula is Cu6Si6O18·6H2O (also reported as CuSiO2(OH)2). It has a hardness o ...
,
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 ...
,
conichalcite Conichalcite, Ca Cu( As O4)(O H), is a relatively common arsenate mineral related to duftite ( PbCu(AsO4)(OH)). It is green, often botryoidal, and occurs in the oxidation zone of some metal deposits. It occurs with limonite, malachite, beudanti ...
and
tenorite Tenorite is a copper oxide mineral with the chemical formula CuO. Occurrence Tenorite occurs in the weathered or oxidized zone associated with deeper primary copper sulfide orebodies. Tenorite commonly occurs with chrysocolla and the copper c ...
. It occurs with primary malachite at the Milpillas Mine in Mexico.Moore and Origlieri (2008) Mineralogical Record 39-6:25-34 The type locality is the Sanda Mine, Mindouli, Pool Region, Republic of Congo.


References


External links

JMol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=00578 {{Commons category Copper(II) minerals Inosilicates