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Marcasite
(FeS2, Iron Sulfide)
- Hardness: 6-6.5
- Metallic luster
- Brassy yellow with a greenish tint
- Multi-color tarnish may exist as the result of oxidation
- Joplin, MO, Grant Co., WI, Hardin Co., IL, Mexico, France, Peru, China, and Russia
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Marcasite, whose name is derived from the Arabic word for pyrite. The two minerals, marcasite and pyrite, are often confused due to their similar characteristics. Marcasite is a polymorph of pyrite which means that it has the same chemistry as pyrite but a different structure and, therefore, different symmetry and crystal shapes. Adding to the confusion between marcasite and pyrite is the use of the word marcasite as a jewelry trade name. The term is applied to small polished and faceted stones that are inlayed in sterling silver.
Marcasite is difficult to distinguish from pyrite when a lack of distinctive crystal habits exists. In fact, many specimens have been wrongly identified as pyrite or marcasite by even experienced mineral collectors. For many years the iron sulfide "Suns" found in Illinois coal mines were called "Marcasite Suns" (also known as "Marcasite Dollars") until X-ray studies showed them to be mostly pyrite. The possibility that they were originally marcasite and then later transformed into pyrite is being studied. Now they are correctly called "Pyrite Suns".
