mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...

, argentite (from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''argentum'', silver) is cubic

silver sulfide Silver sulfide is an inorganic compound with the formula . A dense black solid, it is the only sulfide of silver. It is useful as a photosensitizer in photography. It constitutes the tarnish that forms over time on silverware and other silver obje ...

(Ag₂S), which can only exist at temperatures above 173 °C,Mineralienatlas Lexikon - Argentit (in German)
/ref> 177 °C
/ref> or 179 °C.Argentite on Webmineral
/ref> When it cools to ordinary temperatures it turns into its

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 ...

polymorph,

acanthite 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 . Argentite is the stable form above that temperature. As argentite cools below that tem ...

. The

International Mineralogical Association 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. Th ...

has decided to reject argentite as a proper mineral. The name "argentite" sometimes also refers to

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

s 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. This form of acanthite is occasionally found as uneven

cube In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. Viewed from a corner it is a hexagon and its net is usually depicted as a cross. The cube is the only r ...

s and

octahedra In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic luster. Argentite belongs to the

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cryst ...

group. Cleavage, which is so prominent a feature in galena, here presents only in traces. The mineral is perfectly

sectile Sectility is the ability of a mineral to be cut into thin pieces with a knife. Minerals that are not sectile will be broken into rougher pieces when cut. Metals and paper are sectile. Sectility can be used to distinguish minerals of similar appea ...

and has a shining streak;

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,

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 7.2–7.4. It occurs in mineral veins, and when found in large masses, as in

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

and in the

Comstock Lode The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada (then western Utah Territory), which was the first major discovery of silver ore in the United ...

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

, it forms an important

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...

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 Jalpa is a town located in the Mexican state of Zacatecas, close to the border with Jalisco and Aguascalientes and about a two hours drive south of the capital city, Zacatecas. Jalpa is a colonial-style city, with cobble stone streets, narrow walkw ...

, is known as

jalpaite Jalpaite is a rare copper silver sulfide mineral with formula Ag3CuS2. It was first described in 1858 for an occurrence in the Leonora Mine, Jalpa, Zacatecas, Mexico and named for the locality. It occurs in low temperature hydrothermal veins at t ...

References

External links

{{Authority control Silver minerals Sulfide minerals