About
Marcasite is the most prevalent mineral to experience a condition known as pyrite decay, in which a specimen will slowly disintegrate into a white powder. Little is known about this detrimental condition. It only effects certain specimens at random, while other specimens remain unaffected. However, certain localities are more prone to this condition than others. When a specimen goes through pyrite decay, the sulfur atoms free themselves and form an acid powder that attacks other sulfide minerals and mineral labels. It is most important to remove an afflicted specimen from other minerals, to prevent this condition from spreading.
Crystal Forms & Aggregates
Other ID Marks
Striking Features
Environment
Varieties
✓ common · ✗ uncommon
Polymorphs
Noteworthy Localities
The U.S. has excellent localities for this mineral. The best and most abundant sources are in the midwest, specifically Joplin, Jasper Co., Missouri; the Sweetwater Mine, Ellington, Reynolds Co., Missouri; Picher, Ottawa Co., Oklahoma; and Baxter Springs and Treece, Cherokee Co., Kansas. Other important Marcasite localities include the Rensselaer Quarry, Pleasant Ridge, Jasper Co., Indiana; and Shullsburg, Lafayette Co., Wisconsin. In Canada, good specimens are found at the Lafarge Quarry, Dundas, Wentworth Co., Ontario.
Common Mineral Associations
Distinguishing Similar Minerals
Cobaltite - Lower hardness, forms in different crystals, and usually whiter.
Pyrite - Forms in different crystallizes in different crystal system, though may be very difficult to distinguish when crystals are indistinct.
Pyrrhotite - Lower hardness, darker color, attracted to magnets.
Photos
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