Arsenopyrite

Arsenopyrite is an iron arsenic sulfide (FeAsS). It is a hard (Mohs 5.5-6) metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes. With 46% arsenic content, arsenopyrite, along with orpiment, is a principal ore of arsenic. When deposits of arsenopyrite become exposed to the atmosphere, usually due to mining, the mineral will slowly oxidize, converting the arsenic into oxides that are more soluble in water, leading to  Acid mine drainage.
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Noun
1. a silver-white or gray ore of arsenic
(synonym) mispickel
(hypernym) mineral
(substance-meronym) arsenic, As, atomic number 33

(n.)
A mineral of a tin-white color and metallic luster, containing arsenic, sulphur, and iron; -- also called arsenical pyrites and mispickel.
  

General Information:
 Chemical Formula:
FeAsS
 Composition:
(Molecular Weight = 162.83 gm)
Iron 34.30 % Fe
Arsenic 46.01 % As
Sulfur 19.69 % S 
 Empirical Formula:
Fe3+AsS
 IMA Status:
Approved IMA 1960
 Name Origin:
Named after the minerals chemical composition.
Physical Properties:
 Cleavage:
[110] Distinct
 Color:
tin white or light steel gray.
 Density:
6.07
 Diaphaniety:
Opaque
 Habits:
Striated - Parallel lines on crystal surface or cleavage face., Euhedral Crystals - Occurs as well-formed crystals showing good external form., Prismatic - Crystals Shaped like Slende r Prisms (e.g. tourmaline).
 Hardness:
5 - Apatite
 Luminescence:
None.
 Luster:
Metallic
 Streak:
black
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ARSENOPIRITE. MISPICKEL