Allotropy

Allotropy, occurrence of an element in 2 or more forms (allotropes) that differ in their crystalline or molecular structure. Allotropes may have strikingly different physical or chemical properties. Allotropy in which the forms are stable under different conditions and are reversibly interconvertible at certain temperatures and pressures is called anantiotropy. Notable examples of allotropy are diamond and graphite (allotropes of carbon) and oxygen and ozone.