Marcasite

One of the most interesting bits of information about marcasite is that in some mines, where marcasite is plentiful and the right situation exists (mass versus age and air) the walls can actually feel warm! Of course, a piece of jewelry with small marcasite crystals won't have the critical mass for you to feel the difference. What you may be able to notice is a slight eggy smell since it is an iron sulfide.

If you live in Missouri, Wisconsin and Illinois there is marcasite in the earth around you. Mexico, France, Peru, China and Russia also have deposits. Look for a shiny, sometimes iridescent crystal with a slight olive green tint. It is common to find pyrite (fools gold) masquerading as marcasite especially since they have the same chemistry. You would need a microscope to see their different crystalline structures. But don't worry, as long as you don't think its gold, you should be fine!

Both marcasite and pyrite had their heyday during the Victorian and Art Deco Eras. To show them off, the metal of choice is still sterling. You may recognize the glittery patterns and designs that have echoed over time and are popular in contemporary jewelry. Be gentle with your marcasite. It's a 6-6 1/2 on the Moh's scale. That means no hair spray, perfume, oils, liquid or sonic cleaners. Use a soft, clean polishing cloth to keep it shiny.