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Marcasite
Current inventory:  0 gems
 

Chemistry:  FeS₂  [Iron Sulfide]

Discovered in 1845;   IMA status: Valid (pre-IMA; Grandfathered).
Named in 1845 after an Arabic or Moorish name applied to Pyrite and similar metallic bronze colored minerals.

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/D.20-10

Nickel-Strunz 10th Ed. ID:

9.GD.10

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
E : Metal Sulfides, M: S <= 1:2
B : M:S = 1:2, with Fe, Co, Ni, PGE, etc.

Related to:

Marcasite Group. Marcasite - Iridarsenite Series. Isostructural with Safflorite. A polymorph of Pyrite.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals typically tabular on [010], also pyramidal, prismatic, and, rarely, capillary; curved faces common. Stalactitic, reniform, fine-granular massive; cockscomb and spearhead shapes due to twinning on [101].

Twinning:

Common and repeated on [101]; less common on [011]. Intense twin lamellae development observed in polished section.

Physical Properties

Cleavage:

[101] Distinct, [110] Indistinct (in traces)

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Hardness (Mohs):

6.0 - 6.5

Density:

4.887 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Magnetic after heating

Optical Properties

Color:

Bronze, light Brass Yellow, Tin White

Transparency:

Opaque

Luster:

Metallic

Refractive Index:

None (opaque)

Birefringence:

None (opaque)

Dispersion:

None (opaque)

Pleochroism:

Strong; [100] creamy white; [010] light yellowish white; [001] white with rose-brown tint.

Anisotrophism:

Very Strong; yellow through light green to dark green

Health Warning:

Marcasite is unstable to metastable and decrepitates, altering to melanterite, which contains sulfuric acid. Always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest.

Occurances

Geological 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.

Common Associations:

Calcite, Dolomite, Fluorite, Galena, Pyrite, Pyrrhotite, Sphalerite

Common Impurities:

Cu, As

Type Locality:

n/a

Year Discovered:

1845

View mineral photos:

Marcasite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Marcasite is an attractive metallic mineral. The name Marcasite is derived from the Arabic word for Pyrite. Marcasite is a polymorph of Pyrite which means that it has the chemistry, FeS2, as Marcasite; but a different structure and therefore different symmetry and crystal shapes. Marcasite and Pyrite are often difficult to distinguish from one another due to their similar characteristics.

Marcasite was used by the ancient Greeks and was also polished in large slabs by the Incas of Central America. Marcasite was popular in jewelry in the eighteenth century and the Victorian era but is not very popular currently. It is quite brittle and easily broken. Much of the "Marcasite" in antique jewelry is actually Pyrite.

Marcasite is slightly unstable, and over a period of years of exposure to air, will oxidize, freeing sulfur which forms sulfuric acid. Over a period of decades, most Marcasite specimens will disintegrated into dust. A sulfur smell released during this reaction is an easy characteristic distinguishing Marcasite from Pyrite.

Marcasite is available from many localities worldwide.
 

  
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