Choose one of the following Minerals for more details: Crystal
formations such as this grow out of mineral-rich solutions in
spacious rock cavities. When the solution becomes saturated,
crystals begin to form on rock walls, on other crystals, or even
on particles of dust. They grow quickly or slowly--or stop--
depending on changes in temperature and the concentration of the
solution. Marcasite forms from iron and sulfur to make crystals
with a chemical composition of FeS2. Note how the size of the
forming crystals grew larger with each round of formation in
this specimen.