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Acanthite

Mineral, silver sulfide

Field	Value
name	Acanthite
category	Sulfide mineral
image	Acanthite - Imiter mine, Jbel Saghro, Tinghir, Drâa-Tafilalet, Morocco.jpg
imagesize	280px
caption	Crystallized acanthite (4.0 × 2.5 × 1.5 cm) from Imiter mine, Jbel Saghro mountain range, Morocco
formula	Ag2S
IMAsymbol	Aca
strunz	2.BA.30a
system	Monoclinic
class	Prismatic (2/m)
(same H-M symbol)
symmetry	P21/n
unit cell	a = 4.229 Å, b = 6.931 Å
c = 7.862 Å; β = 99.61°; Z = 4
color	Iron-black
habit	Primary crystals rare, prismatic to long prismatic, elongated along [001], may be tubular; massive. Commonly paramorphic after the cubic high-temperature phase ("argentite"), of original cubic or octahedral habit
twinning	Polysynthetic on {111}, may be very complex due to inversion; contact on {101}
cleavage	Indistinct
fracture	Uneven
tenacity	Sectile
mohs	2.0–2.5
luster	Metallic
streak	Black
diaphaneity	Opaque
gravity	7.20–7.22
references

(same H-M symbol) c = 7.862 Å; β = 99.61°; Z = 4 | length fast/slow = 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. 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.

Occurrence

Acanthite is a common silver mineral in moderately low-temperature hydrothermal veins and in zones of supergene enrichment. It occurs in association with native silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite, galena, chalcopyrite, sphalerite, calcite and quartz.

Acanthite was first described in 1855 for an occurrence in the Jáchymov (Joachimsthal) district, Ore Mountains, Bohemia (today Karlovy Vary Region, Czech Republic). The name is from the Greek "akantha" meaning thorn or arrow, in reference to its crystal shape.

Gallery

File:Acanthite - Chispas Mine, Arizpe, Sonora, Mexico.jpg|Acanthite. Locality: Chispas Mine, Arizpe, Sonora, Mexico. Scale is one inch with a ruled line at one cm. File:Acanthite-180757.jpg| Classic acanthite specimen from the Rayas Mine at Guanajuato, Mexico. Size: 2.4 × 1.1 × 1.1 cm.

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
(2012). "Rocks and Minerals". Dorling Kindersley Limited.
"Acanthite". Mineralogical Society of America.
[http://www.mindat.org/min-10.html Mindat.org]
[https://www.webmineral.com/data/Acanthite.shtml Webmineral data]
Klein, Cornelis and Cornelius S. Hurlbut, ''Manual of Mineralogy,'' Wiley, 20th ed., 1985, pp. 271-2 {{ISBN. 0-471-80580-7

Info: Wikipedia Source

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sulfide-minerals silver-minerals monoclinic-minerals glances minerals-in-space-group-14 minerals-described-in-1855

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