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Argentite
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<p>In <a href="/facts/Mineralogy/MeIK9lx9">mineralogy</a>, argentite is <a href="/facts/Cubic_crystal_system/92Co7BKM">cubic</a> <a href="/facts/Silver_sulfide/muzsPR6v">silver sulfide</a> (Ag2S), which can only exist at temperatures above 173 °C (343 °F), 177 °C (351 °F), or 179 °C (354 °F). When it cools to ordinary temperatures it turns into its <a href="/facts/Monoclinic/5PCwXvzX">monoclinic</a> <a href="/facts/Polymorphism_(materials_science)/bu2tqsB9">polymorph</a>, <a href="/facts/Acanthite/jSxGbILc">acanthite</a>. The <a href="/facts/International_Mineralogical_Association/BzSmsAYQ">International Mineralogical Association</a> has decided to reject argentite as a proper mineral. </p><p>The name "argentite" sometimes also refers to <a href="/facts/Pseudomorph/vSd9JdAY">pseudomorphs</a> 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 <a href="/facts/Cube/65lUaAqN">cubes</a> and <a href="/facts/Octahedron/G38q92xW">octahedra</a>, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic luster. </p><p>Argentite belongs to the <a href="/facts/Galena/eSaK62FA">galena</a> group. <a href="/facts/Cleavage_(crystal)/p4YHe01X">Cleavage</a>, which is so prominent a feature in galena, here presents only in traces. The mineral is perfectly <a href="/facts/Sectility/tPYwGzKn">sectile</a> and has a shining streak; <a href="/facts/Hardness/PtGn6E20">hardness</a> 2.5, <a href="/facts/Specific_gravity/ySquGd2x">specific gravity</a> is 7.2–7.4. It occurs in mineral veins, and when found in large masses, as in <a href="/facts/Mexico/IT5bwhdh">Mexico</a> and in the <a href="/facts/Comstock_Lode/WzUKND0g">Comstock Lode</a> in <a href="/facts/Nevada/HNWhCrQv">Nevada</a>, it forms an important <a href="/facts/Ore/kgc9DssX">ore</a> of silver. The mineral was mentioned in 1529 by <a href="/facts/G._Agricola/FXprFXAK">G. Agricola</a>, but the name <i>argentite</i> was not used till 1845 and is due to <a href="/facts/W._Haidinger/pbeHUQVB">W. Haidinger</a>. Old names for the species are <i>Glaserz</i>, <i>silver-glance</i> and <i>vitreous silver</i>. A related copper-rich mineral occurring e.g. in <a href="/facts/Jalpa,_Zacatecas/D6Jkpcd5">Jalpa, Zacatecas</a>, <a href="/facts/Mexico/IT5bwhdh">Mexico</a>, is known as <a href="/facts/Jalpaite/pAeh1G3T">jalpaite</a>. </p> <ul><li> This article incorporates text from a publication now in the <a href="/facts/Public_domain/YWKMDKw4">public domain</a>: <a href="/facts/Leonard_James_Spencer/yuVCYogn">Spencer, Leonard James</a> (1911). "Argentite". In <a href="/facts/Hugh_Chisholm/2vWblUBe">Chisholm, Hugh</a> (ed.). <i><a href="/facts/Encyclop%C3%A6dia_Britannica_Eleventh_Edition/mPElbCRY">Encyclopædia Britannica</a></i>. Vol. 2 (11th ed.). Cambridge University Press. p. 475.</li></ul>