Marcasite Cocks Comb

Marcasite Cocks Comb. Here's a really attractive and rare classic old stock specimen of Cock’s Comb Marcasite Crystals from the Joplin Missouri Tri-State area. This is an unusual specimen, featuring sharp, truly breathtaking displays of Marcasite Crystals from the now closed sections of the Tri-State District. The Marcasite crystals are on a chert matrix, typical of the area. It's a very good representative specimen from an important productive district of the past.

Excellent examples of this classic are hard to locate these days. For a rare species like Marcasite, this is a large specimen and it displays magnificently. We acquired this specimen from Maggie McShan in Needles, CA before her death a few years ago. It shows slight signs of decay, after spending many decades in a Maggie and Franks collection.

Marcasite, whose name is derived from the Arabic word for pyrite, is a common and an attractive mineral. 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. The marcasite/pyrite polymorph pair is probably the most famous polymorph pair next to the diamond/graphite pair.

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 roster's head crest, hence the name. The habit is very distinctive and can not be mistaken for any other mineral.

Marcasite has been known to pseudo morph other minerals. A pseudo morph is an atom by atom replacement of one mineral's chemistry for another. If done subtly, the replacement can leave the old mineral's shape intact. The effect is one mineral in the shape of another, hence the term pseudo morph (Latin for false shape). Marcasite has pseudo morphed pyrite, gypsum, fluorite and others. At other times Marcasite is pseudo morphed itself into the iron oxide mineral goethite. Often the replacement is only peripheral and leaves a thin skin of iron oxides on the crystals. These iron oxides are seen as iridescencent sheens and can provide Marcasite specimens with quite an attractive and colorful appearance. These oxides may also have a positive effect in slowing marcasite's unfortunate deterioration.

Over a period of years, some Marcasite will oxidize in collections, freeing sulfur which forms sulfuric acid. The acid will then attack the paper label and even the cardboard box holding the specimen. Over a period of decades, most Marcasite specimens will have disintegrated into an undesirable dust along with deteriorated paper scraps.

Because of its age, this specimen seems to be aging so slowly that it will probably last for a lot longer than I'll be alive. Marcasite is an interesting and attractive mineral and even with the slow deterioration can be a pleasure to own for many many years.