In mineralogy, 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 (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. The International Mineralogical Association 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 cubes 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 group. 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 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 at its densest ...

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 Unit ...

Nevada Nevada ( ; ) is a state in the 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. Nevada is the 7th-most extensive, ...

, 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,

, 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