Mineral Information and Data:

Marcasite
FeS2 [CNMNC approved formula]

Named from a word of Arabic or Moorish origin, earlier applied to pyrite and other substances.

IMA status : Valid species (Pre-IMA 1845) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
02.12.02.01  
  (02) Sulfides - Including Selenides and Tellurides
  (02.12) where Am Bn Xp, with (m+n):p=1:2
  (02.12.02) Marcasite Group (Orthorhombic: Pnnm)
  
Nickel-Strunz
(10th edition) :
02.EB.10a
  (02) Sulfides
  (02.E) Metal Sulfides, M:S = 1:2
  (02.EB) M:S = 1:2, with Fe, Co, Ni, PGE, etc.
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 4.443 Å, b = 5.424 Å, c = 3.387 Å
Crystal Habit: Crystals tabular or pyramidal, prismatic or capillary; massive, fine granular; stalactitic; globular; reniform
Twinning: Common on {101}, repeated; also on {011}
  
Color: Pale brass-yellow to tin-white, darkens on exposure
Diaphaneity: Opaque
Luster: Metallic
Hardness (Mohs): 6 to 6.5
Measured Density: 4.92 g/cm3
Cleavage: 2; {101} distinct; {110} traces
Tenacity: Brittle
Fracture: Uneven
Streak: Grayish or brownish black
  
Polymorphism and Series: Dimorphous with pyrite
Geologic Setting: Typically formed under low-temperature highly acidic conditions, both in sedimentary environments (shales, limestones, and low rank coals) and in hydrothermal veins formed by ascending solutions.
Mineral Association: Pyrite, pyrrhotite, galena, sphalerite, fluorite, dolomite, calcite
  
Synonyms/varieties: White iron pyrite
Other Properties: BioMineral.

 

Marcasite
Marcasite on calcite
Origin: Taxco, Guerrero, Mexico
Sample size: 6 x 3.5 x 3.5 cm
Photo: Rob Lavinsky

 

Marcasite
(zoom-in of above)

 

Marcasite
Origin: Belle Fourche Reservoir, Butte County, South Dakota, U.S.A.
Sample size: 5.6 x 4.1 x 4 cm
Photo: John Veevaert, Trinity Mineral Co

 

Marcasite
(zoom-in of above)

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