Chalcophyllite is a rare secondary

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 pinkis ...

arsenate The arsenate ion is . An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resem ...

mineral occurring in the oxidized zones of some

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

-bearing copper deposits. It was first described from material collected in Germany. At one time chalcophyllite from Wheal Tamar in Cornwall, England, was called tamarite, but this name is now discredited (not to be confused with the

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

mineral taramite, which is quite different). At

Wheal Gorland Wheal Gorland was a Wikt:metalliferous, metalliferous mine located just to the north-east of the village of St Day, Cornwall, in England, United Kingdom. It was one of the most important Cornish mines of the late 18th and early 19th centuries, b ...

a specimen exhibiting partial replacement of liriconite, , by chalcophyllite has been found. The mineral is named from the Greek, ''chalco'' "copper" and ''fyllon'', "leaf", in allusion to its composition and platy structure. It is a classic Cornish mineral that can be confused with tabular spangolite.

Formula

Two different formulae are quoted in the literature for chalcophyllite, (molar mass 3098 g) and (molar mass 2956 g). The difference reflects the fact that the water content varies at room temperature based on relative humidity.

Unit cell

Chalcophyllite crystallizes in the

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crysta ...

crystal class In crystallography, a crystallographic point group is a set of symmetry operations, corresponding to one of the point groups in three dimensions, such that each operation (perhaps followed by a translation) would leave the structure of a crystal u ...

, 3 2/m with

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

R 3m or with space group R . Some authors choose a unit cell with three

formula unit In chemistry, a formula unit is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. Exa ...

s per cell (Z=3), and some a smaller unit cell with only 1.5 formula units per cell (Z=1.5). For the larger unit cell a = 10.77 Å, c = 57.5 Å, Z=3.Corbett (1973) American Mineralogist 58: 792–793 For the smaller unit cell c is only half as long, a = 10.756 Å, c = 28.678 Å, Z = 1.5.

Crystal habit

Crystals are platy, six-sided and flattened perpendicular to the c

crystal axis In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns t ...

, and may be striated triangularly on these flattened faces. It may form rosettes, or be drusy, foliated or massive.

Physical properties

Cleavage is perfect perpendicular to the c crystal axis, and twinning occurs with as the twin plane. Fracture is irregular. 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 ...

only 2, the same as

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 drywall. ...

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 (molecule), wa ...

is generally given in the range 2.67 to 2.69, but Webmineral has 2.4 to 2.66. Chalcophyllite is soluble in acids and in ammonia. It is not

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

, nor

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

. The water content varies at room temperature based on

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

. Chalcophyllite alters to

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 as ...

, which is a copper-aluminium silicate with the formula .

Optical properties

Many copper minerals are blue or green in color; chalcophyllite is blue-green to emerald-green, with a pale green streak and vitreous to subadamantine luster, pearly on . Crystals are transparent to translucent. It is

uniaxial In crystal optics, the index ellipsoid (also known as the ''optical indicatrix'' or sometimes as the ''dielectric ellipsoid'') is a geometric construction which concisely represents the refractive indices and associated polariz ...

(-) with

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

n_ω = 1.618 to 1.632 and n_ε = 1.552 to 1.575. Indices of refraction vary markedly depending on the relative humidity since the water content varies at ambient temperature. It 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 O blue-green and E almost colorless.

Environment

Chalcophyllite is an uncommon secondary mineral occurring in the oxidized zones of some

-bearing

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

copper deposits. Associated minerals include

azurite Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the Type locality (geology), type locality at Chessy, Rhône, Chessy-les-Mines near ...

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 fractures ...

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 ...

, spangolite,

connellite Connellite is a rare mineral species, a hydrous copper chloro-sulfate, Cu19(OH)32(SO4)Cl4·3H2O, crystallizing in the hexagonal system. It occurs as tufts of very delicate acicular crystals of a fine blue color, and is associated with other copp ...

cuprite Cuprite is an oxide mineral composed of copper(I) oxide Cu2O, and is a minor ore of copper. Its dark crystals with red internal reflections are in the isometric system hexoctahedral class, appearing as cubic, octahedral, or dodecahedral forms, o ...

, cyanotrichite,

strashimirite Strashimirite ( IMA symbol: Ssh) is a rare monoclinic mineral containing arsenic, copper, hydrogen, and oxygen. It has the chemical formula Cu8(AsO4)4(OH)4·5(H2O). This mineral was discovered in Zapachitsa (Zapacica) copper deposit, Svoge, Sofi ...

, parnauite,

lavendulan Lavendulan is an uncommon copper arsenate mineral, known for its characteristic intense electric blue colour. It belongs to the lavendulan group, which has four members: * Lavendulan NaCaCu5(AsO4)4Cl.5H2O * Lemanskiite NaCaCu5(AsO4)4Cl.5H2O * Sam ...

cornubite Cornubite is a rare secondary copper arsenate mineral with formula: Cu5(AsO4)2(OH)4. It was first described for its discovery in 1958 in Wheal Carpenter, Gwinear, Cornwall, England, UK.Claringbull, Hey and Davis, ''American Mineralogist'' (1959) 4 ...

, langite,

clinoclase Clinoclase is a hydrous copper arsenate mineral, Cu3AsO4(OH)3. Clinoclase is a rare secondary copper mineral and forms acicular crystals in the fractured weathered zone above copper sulfide deposits. It occurs in vitreous, translucent dark blue to ...

pharmacosiderite Pharmacosiderite is a hydrated basic ferric arsenate, with chemical formula K Fe4( As O4)3(O H)4·(6-7) H2O and a molecular weight of 873.38 g/mol. It consists of the elements arsenic, iron, hydrogen, potassium, sodium and oxygen. It has a M ...

and

mansfieldite Mansfieldite is an uncommon mineral that was named after an american geologist, George Rogers Mansfield. It has been considered a valid specie since 1948. It's a member of the variscite group. Mansfieldite creates a series with scorodite, and it i ...

. The type material is conserved at the Mining Academy, Freiberg, Germany. Notable occurrences include the Majuba Hill Mine, Antelope District, Nevada, US and Cornwall, including

, UK.

References

External links

{{Commons category
Crystal structure of Chalcophyllite
Arsenate minerals Copper(II) minerals Trigonal minerals Minerals in space group 148