1.8" Nipomo Marcasite Agate Oval Cabochon

Agate is a variety of microcrystalline quartz (chalcedony) that displays translucence and in some cases banding. Agate primarily forms when silica-rich fluids fill pockets within rock and/or fossils, resulting in deposition of the silica along the walls of the rock. This process can result in banding patterns as the composition and impurities of the fluids change over time. These banding patterns can either form as flat layers or rounded layers, depending on the surfaces available for deposition.

Marcasite is an iron sulfide mineral with the chemical formula FeS2. It is similar to pyrite in both its chemical composition and appearance, however it forms with a different crystal structure and is much more reactive to humidity. It is often found within sedimentary rock and hydrothermal deposits, and at one point was used for its sulfur content.