Over a period of decades, most marcasite specimens will have disintegrated into an undesirable dust along with deteriorated paper scraps. A sulfur smell released during this reaction is often the easiest characteristic distinguishing Marcasite from Pyrite. The reaction is triggered by exposure to air and is an exothermic reaction, meaning that the reaction releases heat. This does not mean that marcasite hand specimens will feel warm to the touch, but in some marcasite rich portions of certain mines the mine walls would get too hot to touch because of this reaction. Either way marcasite is an interesting and attractive mineral and even with the slow deterioration can be a pleasure to own for many many years.
Color is brassy yellow with a greenish tint at times.
A multi-colored tarnish may exist that is the result of oxidation. Luster is metallic. Crystals are opaque. Crystal Habits include the tabular, bladed or prismatic forms. Also massive, botryoidal, stalactitic and nodular.