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www.mineralgallery.co.za Minerals K-O |
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Marcasite |
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Name
Marcasite
Chemistry
FeS2, Iron Sulfide
Uses
As a minor ore of iron and as a mineral specimen, also in jewelry
Color
Brassy yellow with a greenish tint at times. A multi-colored tarnish may exist that is the result of oxidation.
Hardness
6-6.5
Specific gravity
4.8
Marcasite is a very interesting mineral.
When exposed to the atmosphere it starts to tarnish and oxidizes. It will oxidize down to a powder after many decades.
The iron sulfide mineral marcasite has the same chemical composition as its more stable and common cousin pyrite. Marcasite is a polymorph of iron pyrite which means it shares the same chemical make-up as iron pyrite. It forms a different habit but can also form psuedomorphs that looks like the original pyrite. That is why it is often difficult to distinguish between marcasite and iron pyrite.
With similar hardness (6 to 6 1/2) and specific gravity (4.89 for marcasite, 5.0 for pyrite), marcasite is distinguished from pyrite by its pale yellow color and its tabular crystals (orthorhombic system), which are often twinned, producing a hacksaw appearance. It is found in ore veins and in sedimentary rocks as replacement deposits and concretions.
Marcasite is used in semiprecious jewelry, with many small, faceted stones set in silver to create a reflective sparkle.
