Acanthite
| Acanthite | |
|---|---|
 Crystallized acanthite (4.0 × 2.5 × 1.5 cm) from Imiter mine,Jbel Saghromountain range, Morocco | |
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | Ag2S |
| IMA symbol | Aca[1] |
| Strunz classification | 2.BA.30a |
| Crystal system | Monoclinic[2] |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | P21/n |
| Unit cell | a = 4.229 Å, b = 6.931 Å c = 7.862 Å; β = 99.61°; Z = 4 |
| Identification | |
| Color | Iron-black |
| Crystal 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 scalehardness | 2.0–2.5 |
| Luster | Metallic |
| Streak | Black |
| Diaphaneity | Opaque |
| Specific gravity | 7.20–7.22 |
| References | [3][4][5][6] |
Acanthiteis a form ofsilver sulfidewith the chemical formula Ag2S. It crystallizes in themonoclinicsystem and is the stable form of silver sulfide below 173 °C (343 °F).Argentiteis 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.[3][6]Acanthite is the only stable form in normal air temperature.
Occurrence[edit]
Acanthite is a common silver mineral in moderately low-temperaturehydrothermal veinsand in zones ofsupergeneenrichment. It occurs in association with native silver,pyrargyrite,proustite,polybasite,stephanite,aguilarite,galena,chalcopyrite,sphalerite,calciteandquartz.[3]
Acanthite was first described in 1855 for an occurrence in theJáchymov(Joachimsthal) district,Ore Mountains,Bohemia(todayKarlovy Vary Region,Czech Republic). The name is from the Greek "akantha" meaning thorn or arrow, in reference to its crystal shape.[4][5][6]
Gallery[edit]
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Classic acanthite specimen from the Rayas Mine atGuanajuato,Mexico. Size: 2.4 × 1.1 × 1.1 cm.
See also[edit]
References[edit]
- ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
- ^Bonewitz, Ronald Louis (2012).Rocks and Minerals.Dorling Kindersley Limited.ISBN978-0-7566-9042-7.
- ^abcAnthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.)."Acanthite"(PDF).Handbook of Mineralogy.Chantilly, VA: Mineralogical Society of America.
- ^abMindat.org
- ^abWebmineral data
- ^abcKlein, Cornelis and Cornelius S. Hurlbut,Manual of Mineralogy,Wiley, 20th ed., 1985, pp. 271-2ISBN0-471-80580-7
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