Hematite is a totally opaque gem that looks very much like polished metal. It is found in grey, blue and black hues, called deriving its colors from its origins near iron mining areas rich in metallic minerals. It is a form of iron oxide and can often be mistaken for polished silver, due to its deeply dark undertones. Marcasite, on the other hand, is a distant relative of hematite, but its color-formation is very different. It has reddish undertones that give it a ruddy, rust-color effect. Both of these materials aren't expensive and are rarely mounted in any setting. Instead, they are normally used as mounting material, costume jewelry or inexpensive decorations applied to richer pieces.