Marcasite is a mineral that is composed of iron sulfide (FeS2) and is similar in chemical composition to pyrite, also known as "fool's gold". Marcasite has a bright metallic luster and a brass-yellow to silver-gray color that can sometimes resemble silver. It is relatively soft and brittle, with a hardness of about 6 to 6.5 on the Mohs scale.

Marcasite is often used in jewelry as a substitute for more expensive materials, such as diamonds or silver. It is popular in vintage and antique jewelry, particularly in Art Deco and Victorian styles. Marcasite jewelry often features small, faceted stones that are set in silver or other metals and can be used to create intricate designs.

One of the unique properties of marcasite is that it can easily tarnish and become discolored over time, particularly if it comes into contact with moisture or chemicals. This can give marcasite jewelry an aged, vintage look that is highly sought after by collectors and enthusiasts.

While marcasite is a popular material for jewelry making, it is important to note that it can be quite fragile and brittle, and care should be taken when handling and cleaning marcasite pieces.