Djurleite is a copper sulfide mineral of secondary origin with formula Cu₃₁S₁₆ that crystallizes with

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 ...

-prismatic symmetry. It is typically massive in form, but does at times develop thin tabular to prismatic crystals. It occurs with other supergene minerals such as chalcocite, covellite and digenite in the enriched zone of copper

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...

bodies. It is a member of the chalcocite group, and very similar to chalcocite, Cu₂S, in its composition and properties, but the two minerals can be distinguished from each other by x-ray powder diffraction. Intergrowths and transformations between djurleite, digenite and chalcocite are common.Pósfai, M. & Buseck, P. R. (1994): Djurleite, digenite, and chalcocite: Intergrowths and transformations. American Mineralogist, 79, 308-315 Many of the reported associations of digenite and djurleite, however, identified by powder diffraction, could be anilite and djurleite, as anilite transforms to digenite during grinding. Djurleite was named for the Swedish chemist Seved Djurle (1928–2000), from the

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, Sweden, who first synthesized the mineral in 1958, prior to its discovery in nature. The natural material was first described in 1962 by E H Roseboom Jr, of the

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, from occurrences at the type locality, Barranca del Cobre, Chihuahua, Mexico.Roseboom, E.H. (1962) Djurleite, Cu_1.96S, a new mineral. American Mineralogist: 47: 1181-1184.

The chalcocite group

The chalcocite group is a group of closely related copper sulfides, with the formulae: * Chalcocite (two polymorphs) Cu₂S * Djurleite Cu₃₁S₁₆ (Cu_1.94S) * Digenite (Cu_1.80S) * Roxbyite (Cu_1.78S) * Anilite Cu₇S₄ (Cu_1.75S) * Geerite Cu₈S₅ (Cu_1.60S) * Spionkopite (Cu_1.32S) * Covellite (CuS)

Unit cell

Djurleite has a

structure with a large

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

containing 248

copper Copper is a chemical element; it has symbol Cu (from Latin ) 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-orang ...

and 128

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

atoms.H. T. Evans "Djurleite (Cu1.94S) and Low Chalcocite (Cu₂S): New Crystal Structure Studies
Science 203 (1979) 356
/ref> The formula is Cu₃₁S₁₆,

molar mass In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...

2483 g, and there are 8 formula units per unit cell (Z = 8). The crystal class is 2/m, meaning the structure has an axis of twofold rotational symmetry perpendicular to a mirror plane. The

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

is P2₁/c, and the unit cell parameters are a = 26.897 Å, b = 15.745 Å, c = 13.565 Å and β = 90.13°. The structure is based on hexagonal closest packing of sulfur atoms with a monoclinic space group.Klein et al (1993) Manual of Mineralogy 21st Edition, Wiley

Physical properties

Crystals are short prismatic and thick tabular, but the mineral usually occurs in a massive and compact form. There is no

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 ...

. Pseudohexagonal

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are common, with crystal blocks rotated around the a crystal axis, which is normal to the

close-packed In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occ ...

layers, by multiples of 60°. Djurleite is brittle, with a conchoidal (shell-like)

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 ...

. It is a soft mineral, 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 ...

to 3, a little less than that of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. The

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 ...

, 5.63, is high, due to the copper content, djurleite is denser than the copper-iron sulfide bornite, but not as dense as the iron-arsenic sulfide arsenopyrite.

Optical properties

Djurleite is grey, blue-black or black, with a black streak and a submetallic to metallic luster. It is an opaque mineral, so

refractive indices In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

are not defined. The reflectivity (the percentage of incident energy which is reflected from a surface) for light of

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

540 nm varies between 29.6 and 30.2, and is slightly dependent on the direction of the incident light, that is to say, the mineral is weakly

anisotropic Anisotropy () is the structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit ver ...

Environment

Djurleite is a widely distributed but little known ore mineral of copper, found in the secondary enrichment zones of

deposits, associated with other secondary copper sulfides digenite, chalcocite, bornite,

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a Mohs scale, hardness of 3.5 to 4 ...

and anilite with

pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

Occurrence

The type locality is Barranca de Cobre, Chihuahua, Mexico, and the type material is conserved at the

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, Toronto, Canada, M25369, and at the

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, Washington, DC, US.

References

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External links

* JMol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=10818 Sulfide minerals Copper(I,II) minerals Monoclinic minerals Minerals in space group 14