Marcasite is a mineral formed from iron sulfate. It is occasionally called white pyrite, but is not pyrite, or fool’s gold, as it is sometimes called. To further confuse matters, most gems called marcasite, are in reality pyrite. True marcasite disintegrates quickly and does not keep well in gem form.
The non-gem marcasite is yellow and may exhibit some green tints. It may also have white or brown colorations. It is a relatively soft stone with a hardness of approximately 6-6.5 on the Moh’s Hardness scale. It forms into what are called coxcomb aggregates, where the crystals are separated into crystals that are similar in shape to the head of a top of a rooster’s head. Because of this special formation, marcasite is prized in collections.
Unfortunately, collected marcasite deteriorates gradually, possibly as a result of bacteria. Bacterial agents found abundantly in the air may facilitate the breakdown of iron sulfate. Eventually, a piece of marcasite will completely deteriorate into white powder. One decaying marcasite may affect other minerals close to it. Marcasite specimens tend to be separated to slow down decay of this delicate but attractive mineral.
Marcasite gems or pyrite are steeped in lore and tradition. They are thought to be able to discharge negative energy, improve one’s communication abilities, and protect those who perform dangerous jobs. Such lore tends to be the result of pagan traditions.
Miners, however, often viewed pyrite negatively since it had a deceptive appearance, which many mistook for gold. Many based their opinions on where to dig or pan based on pyrite, and too late learned that these stones were worthless. Thus it inherited the name fool’s gold.
Today marcasite/pyrite gems are of value because they are an attractive black that appears iridescent in the light. They are also very inexpensive, with loose stones of several carats usually less than one US dollar (USD). Those who make their own jewelry often enjoy using pyrite because of its lovely appearance and low cost.