Orpiment

Formula: As2S3

Origin of name: from Latin auripigmentum = golden paint

 

Crystal system: monoclinic

Crystal class: 2/m

Twinning: on {100}

Unit cell: a = 11.49 Å, b = 9.59 Å, c = 4.25 Å, b = 90.5°

 

Colour: yellow, yellow-orange, brownish yellow

Diaphaneity: 

Luster: resinous, pearly on cleavage

Habit: crystals short prismatic, elongated on c-axis, granular, foliated or powdery aggregates, columnar, reniform

Hardness: 1.5 to 2

Specific gravity: 3.49

Cleavage: 2; {010} perfect, {100} traces

Tenacity: sectile, cleavage lamellae

Streak: pale yellow

 

Synonyms/varieties:

 

Comments: 

 

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