Marcasite

Marcasite is generally safe to handle. However, it reacts with water or moisture in the air, releasing irritating sulfuric acid. Avoid getting marcasite wet, wash hands after handling it, and store it in a dry place with low humidity (below 60% is ideal). When cutting or polishing marcasite, wear a dust mask to prevent lung irritation from dust inhalation.

Marcasite exhibits poor toughness, being prone to breaking, chipping, or cracking easily due to its inherent cleavage and brittle internal structure.

Marcasite's propensity for degradation when exposed to water, heat, chemicals, and sweat makes it unsuitable for daily use where such exposures are common.

Blueite (S.H.Emmons): Nickel variety of marcasite, found in Denison Drury and Townships, Sudbury Dist., Ontario, Canada.

Lonchidite (August Breithaupt): Arsenic variety of marcasite, found at Churprinz Friedrich August Erbstolln Mine (Kurprinz Mine), Großschirma Freiberg, Erzgebirge, Saxony, Germany; ideal formula Fe(S, As)₂

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Synonyms for this variety:

kausimkies,

kyrosite,

lonchandite,

metalonchidite (Sandberger) described at Bernhard Mine near Hausach (Baden), Germany.

Sperkise : designates a marcasite having twin spearhead crystal on {101}. Sperkise derives from the German Speerkies (Speer meaning spear and Kies gravel or stone). This twin is very common in the marcasite of a chalky origin, particularly those from the Cap Blanc Nez.

Marcasite can be formed as both a primary or a secondary mineral. It typically forms under low-temperature highly acidic conditions. It occurs in sedimentary rocks (shales, limestones and low grade coals) as well as in low temperature hydrothermal veins. Commonly associated minerals include pyrite, pyrrhotite, galena, sphalerite, fluorite, dolomite, and calcite. As a primary mineral it forms nodules, concretions, and crystals in a variety of sedimentary rock, such as in the chalk layers found on both sides of the English Channel at Dover, Kent, England, and at Cap Blanc Nez, Pas de Calais, France, where it forms as sharp individual crystals and crystal groups, and nodules (similar to those shown here). As a secondary mineral it forms by chemical alteration of a primary mineral such as pyrrhotite or chalcopyrite.

Marcasite was historically mined and refined as a source of sulfur. However, this mineral does not have any practical applications in modern times. Some interesting specimens may be sought out by mineral collectors.