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. They have a habit that looks like marcasite. The possibility that they were originally marcasite and then later transformed into pyrite is being studied. Now they are correctly called "Pyrite Suns", but the confusion still exists. Many marcasite specimens are distinctive enough to reveal their true identity and make interesting and beautiful display specimens.

The most famous habit for marcasite is its "cock's comb" twinned habit. The crystals appear like a rooster's head crest, hence the name. The habit is very distinctive and can not be mistaken for any other mineral. For the past years, these marcasite cut stones have been used in the jewelry industry to make marcasite jewelry have an antique look.

Marcasite and cut steel jewelry were the Georgian (1714-1837) equivalent of costume jewelry.  Cut-steel, like the mineral marcasite, was initially used as a substitute for diamonds.  Early cut steel was faceted in a pyramid shape with flat backs and then individually riveted into place on a mounting. The stone known as Marcasite is actually pyrite which is an iron sulfite.  When pyrite is faceted, its luster is metallic, and the brilliance comes form light reflecting off the facets.  Genuine marcasites are usually set with metal holding the stones in place, inexpensive pieces are often glued into cast mountings.