Marcasite is related to pyrite because it has the same chemical formula and is therefore made of the same elements. Marcasite can become the subject of a process called "pyrite decay". This will transform the marcasite into a white powder. Because of a reaction with the moist from the air, sulphuric acid forms that causes the decay by desintegrating the other sulphuric bonds in the mineral. (See the photos below for the result of this. They are two different marcasite spheres.)Top
Chemical & Physical Information
|Chemical Name||Iron Disulfide|
|Molar mass||119.98 g·mol-1|
|Colour||Bronze yellow to tin white|
|Streak||Green like to black grey|
|Extra||Can decay to a white powder.|
 Specimen from my personal collection, photo taken by me.