白铁矿与黄铁矿（FeS₂）同是同质多象变体，晶体常呈板状，集合体为矛头状或鸡冠状。

产于热液脉状矿床和沉积岩中，有时用于制造硫酸。

The mineral marcasite, sometimes called white iron pyrite, is iron sulfide (FeS₂) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide S₂ ion having a short bonding distance between the sulfur atoms. The structures differ in how these di-anions are arranged around the Fe cations. Marcasite is lighter and more brittle than pyrite. Specimens of marcasite often crumble and break up due to the unstable crystal structure.