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Acanthite

MNHN N°206.101

visu_53 infos

FROM : Imiter mines, Djebel, Sahro, Morroco
SIZE : 6.7 x 4.3 cm

general description

This specimen shows an aggregate of pseudo-octahedral crystals, gray-black to black in colour. The octahedral crystals measure 1.5 cm on average while this sample measures 6.7 x 4.3 cm.

This acanthite is a pseudomorphosis over argentite (also a silver sulphide). Native silver filaments can be seen between the octahedral crystals.

This specimen comes from the Imiter mines, famous for their silver-bearing mineral deposits. The Muséum national d’Histoire naturelle obtained this specimen thanks to support from Total. It is kept in the storage rooms of the collections (i.e., not yet displayed to the public).

Photography: Louis-Dominique Bayle, © MNHN.

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Identity card

SPECIE : Acanthite

HISTORY : Name inspired by the Greek word "ακαντα" [akanta] meaning "arrow", in reference to its crystal shapes

Species first described in 1855 by Gustav Adolf Kenngott (1818-1897), Swiss mineralogist

Type-locality: Jachimov, Czech Republic

CHEMICAL FORMULA : Ag2 S
CRYSTAL SYSTEM : Monoclinic
COLOR : Black, grayish
DIAPHANIETY : Opaque
LUSTER : Metallic
STREAK : Lead gray
MORPHOLOGY : Crystals sometimes prismatic, more often cubo-octahedric
HARDNESS : 2,0-2,5
DENSITY : 7,24

CHEMICAL CLASS : III - Sulfides, arsenides
GROUP : Acanthite
STRUNZ CLASS BEFORE 2001 : 2/B.05-10
STRUNZ CLASS AFTER 2001 : 2.BA.25

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