Argentite

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Argentite sample Argentite.jpg
Argentite sample
The unit cell of argentite Argentite-unit-cell-3D-balls.png
The unit cell of argentite

In mineralogy, argentite (from the Latin argentum, silver) is cubic silver sulfide (Ag2S), which can only exist at temperatures above 173 °C, [1] 177 °C [2] or 179 °C. [3] When it cools to ordinary temperatures it turns into its monoclinic polymorph, acanthite. [2] [3] Argentite belongs to the galena group.

Mineralogy Scientific study of minerals and mineralised artifacts

Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical properties of minerals and mineralized artifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, and ultimately from the Phoenician alphabet.

Cubic crystal system lattice point group

In crystallography, the cubiccrystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.

Contents

The name "argentite" sometimes also refers to pseudomorphs of argentite: specimens of acanthite which still display some of the outward signs of the cubic crystal form, even though their actual crystal structure is monoclinic due to the lower temperature. [2] [1] This form of acanthite is occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic luster. [4]

Pseudomorph mineral or mineral compound that appears in an atypical form

In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form, resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another. The name literally means "false form".

Cube A geometric shape with 6 square faces

In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex.

Octahedron Polyhedron with 8 faces

In geometry, an octahedron is a polyhedron with eight faces, twelve edges, and six vertices. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex.

Cleavage, which is so prominent a feature in galena, here presents only in traces. The mineral is perfectly sectile and has a shining streak; hardness 2.5, specific gravity is 7.2–7.4. It occurs in mineral veins, and when found in large masses, as in Mexico and in the Comstock Lode in Nevada, it forms an important ore of silver. The mineral was mentioned in 1529 by G. Agricola, but the name argentite was not used till 1845 and is due to W. Haidinger. Old names for the species are Glaserz, silver-glance and vitreous silver. A related copper-rich mineral occurring e.g. in Jalpa, Zacatecas, Mexico, is known as jalpaite. [4]

Cleavage (crystal) tendency of crystalline materials to split along definite crystallographic structural planes

Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye.

Sectility is the ability to be cut into pieces. Metals and paper are sectile.

Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. Some materials are harder than others. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.

Rejection by the International Mineralogical Association

The International Mineralogical Association has decided to reject argentite as a proper mineral. [3]

Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. The IMA is affiliated with the International Union of Geological Sciences (IUGS).

Related Research Articles

Galena Rocksalt group, sulfide mineral

Galena, also called lead glance, is the natural mineral form of lead(II) sulfide. It is the most important ore of lead and an important source of silver.

Silver sulfide chemical compound

Silver sulfide is the sulfide of silver. It is useful as a photosensitizer in photography.

Leucite Potassium and aluminium tectosilicate mineral

Leucite is a rock-forming mineral composed of potassium and aluminium tectosilicate K[AlSi2O6]. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhombic or monoclinic individuals, which are optically biaxial and repeatedly twinned, giving rise to twin-lamellae and to striations on the faces. When the crystals are raised to a temperature of about 500 °C they become optically isotropic and the twin-lamellae and striations disappear, although they reappear when the crystals are cooled again. This pseudo-cubic character of leucite is very similar to that of the mineral boracite.

Stilbite stilbite series, zeolite

Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:

Sylvanite telluride mineral

Sylvanite or silver gold telluride, (Ag,Au)Te2, is the most common telluride of gold.

Acanthite mineral, silver sulfide

Acanthite is a form of silver sulfide with the chemical formula Ag2S. It crystallizes in the monoclinic system and is the stable form of silver sulfide below 173 °C (343 °F). Argentite is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C acanthite forms directly. Acanthite is the only stable form in normal air temperature.

Anhydrite mineral, anhydrous calcium sulfate

Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

Pyrrhotite sulfide mineral; polytypes: 11H, 3T, 4C, 4H, 4M, 5C, 6C, 6M, 7H

Pyrrhotite is an iron sulfide mineral with the formula Fe(1-x)S. It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content increases, and troilite is non-magnetic.

Zippeite uranyl sulfate mineral

Zippeite is a hydrous potassium uranium sulfate mineral with formula: K4(UO2)6(SO4)3(OH)10·4(H2O). It forms yellow to reddish brown monoclinic-prismatic crystals with perfect cleavage. The typical form is as encrustations and pulverulent earthy masses. It forms as efflorescent encrustations in underground uranium mines. It has a Mohs hardness of 2 and a specific gravity of 3.66. It is strongly fluorescent yellow in UV radiation and is a radioactive mineral.

Hübnerite oxide mineral

Hübnerite or hubnerite is a mineral consisting of manganese tungsten oxide (chemical formula: MnWO4, it isn't a tungstate). It is the manganese endmember of the manganese - iron wolframite solid solution series. It forms reddish brown to black monoclinic prismatic submetallic crystals. The crystals are typically flattened and occur with fine striations. It has a high specific gravity of 7.15 and a Mohs hardness of 4.5. It is transparent to translucent with perfect cleavage. Refractive index values are nα=2.170 - 2.200, nβ=2.220, and nγ=2.300 - 2.320.

Pyrargyrite sulfosalt mineral

Pyrargyrite is a sulfosalt mineral consisting of silver sulfantimonide, Ag3SbS3. Known also as dark red silver ore or ruby silver, it is an important source of the metal.

Stephanite sulfosalt mineral

Stephanite is a silver antimony sulfosalt mineral with formula: Ag5SbS4 It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal.

Leadhillite carbonate-sulfate mineral

Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb4SO4(CO3)2(OH)2. Leadhillite crystallises in the monoclinic system, but develops pseudo-hexagonal forms due to crystal twinning. It forms transparent to translucent variably coloured crystals with an adamantine lustre. It is quite soft with a Mohs hardness of 2.5 and a relatively high specific gravity of 6.26 to 6.55.

Linarite sulfate mineral

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 sulfate hydroxide with formula PbCuSO4(OH)2. Linarite occurs as monoclinic prismatic to tabular crystals and irregular masses. It is easily confused with azurite, but does not react with dilute hydrochloric acid as azurite does. It has a Mohs hardness of 2.5 and a specific gravity of 5.3 - 5.5.

Aguilarite sulfide mineral

Aguilarite is an uncommon sulfosalt mineral with formula Ag4SeS. It was described in 1891 and named for discoverer Ponciano Aguilar.

Alabandite rocksalt group, sulfide mineral

Alabandite or alabandine is a rarely occurring manganese sulfide mineral. It crystallizes in the cubic crystal system with the chemical composition Mn2+S and develops commonly massive to granular aggregates, but rarely also cubic or octahedral crystals to 1 cm.

Dyscrasite antimonide mineral

The silver antimonide mineral dyscrasite has the chemical formula Ag3Sb. It is an opaque, silver white, metallic mineral which crystallizes in the orthorhombic crystal system. It forms pyramidal crystals up to 5 cm (2.0 in) and can also form cylindrical and prismatic crystals.

Semseyite sulfosalt mineral

Semseyite is a rarely occurring sulfosalt mineral and is part of the class of lead antimony sulfides. It crystallizes in the monoclinic system with the chemical composition Pb9Sb8S21. The mineral forms dark gray to black aggregates.

Jalpaite sulfide mineral

Jalpaite is a rare copper silver sulfide mineral with formula Ag3CuS2.

Pearceite sulfosalt mineral

Pearceite is one of the four so-called "ruby silvers", pearceite Cu(Ag,Cu)6Ag9As2S11, pyrargyrite Ag3SbS3, proustite Ag3AsS3 and miargyrite AgSbS2. It was discovered in 1896 and named after Dr Richard Pearce (1837–1927), a Cornish–American chemist and metallurgist from Denver, Colorado.

References

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Leonard James Spencer CBE FRS was a British geologist. He was an Honorary member of the Royal Geological Society of Cornwall, and also a recipient of its Bolitho Medal. He was president of the Mineralogical Society of Great Britain and Ireland from 1936 to 1939. In mineralogy Spencer was an original investigator who described several new minerals, including miersite, tarbuttite and parahopeite. He also did important work as a curator, editor and bibliographer. He was the third person to receive the Roebling Medal, the highest award of the Mineralogical Society of America.

<i>Encyclopædia Britannica</i> Eleventh Edition 11th edition of Encyclopædia Britannica

The Encyclopædia Britannica Eleventh Edition (1910–11) is a 29-volume reference work, an edition of the Encyclopædia Britannica. It was developed during the encyclopaedia's transition from a British to an American publication. Some of its articles were written by the best-known scholars of the time. This edition of the encyclopedia, containing 40,000 entries, is now in the public domain, and many of its articles have been used as a basis for articles in Wikipedia. However, the outdated nature of some of its content makes its use as a source for modern scholarship problematic. Some articles have special value and interest to modern scholars as cultural artifacts of the 19th and early 20th centuries.