Where Does Marcasite Come From?
Marcasite is a shiny stone often associated with jewelry production, intricate pieces found in estate sales or set into art deco designs. It received its name in 1845, from Arabic or Moorish origins, in honor of its metallic, bronze appearance. Today's chocolate diamond designs resemble antique marcasite pieces, sharing similar color and the period's intricate settings. However, any jewelry labeled marcasite instead sports its look-alike, pyrite. Authentic marcasite stone is too brittle and chemically unstable to be set into jewelry. Does this Spark an idea?
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Where is It Found?
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Mined from sedimentary rocks and coal beds, Marcasite forms in high-alkaline content and low-temperature regions and is found close to surface environs. It usually appears in the same origins as galena, pyrrhotite, sphalerite, fluorite, calcite and dolomite, specifically near Joplin, Missouri, and the surrounding area. Marcasite is a primary and secondary mineral, and it is common in sedimentary rocks such as shale, limestone and low-grade coal beds. It has the same chemical formula as pyrite, but crystallizes differently, so it fits a separate category. A version called cocks comb, or cockscomb -- with elongated crystals that resemble a rooster's head -- hails from Guanajuato, Mexico.
What to Look For
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Marcasite forms crystals, ranging from pale yellow or white to metallic brass-yellow. The crystals darken, or tarnish, to deep yellow or brown with a black streak. The thick, flat, usually tabular -- or pyramidal-shaped -- crystals result in cockscomb fossils.
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Alternative Sources
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Also found in sharp, individual crystals and crystal groups in Dover, Kent, England, marcasite has a primary mineral makeup similar to that of chalk. In its secondary alteration, it forms where chemicals changes occur, like those of pyrrhotite or chalcopyrite.
Caution When Handling
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Considered unstable to metastable, some marcasite reacts to moisture in the air and breaks down to sulfuric acid and iron sulfate -- appearing as a white powder, through a process called pyrite decay. Inhaling the dust, or otherwise ingesting it, is dangerous, so handlers should wash their hands after touching marcasite and avoid breathing the dust. Other minerals can be affected by this chemical change, so they should be stored apart from marcasite.
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References
- Photo Credit mineral image by Marek Kosmal from Fotolia.com
