əˈlä.trəpē noun
also al·lot·ro·pism -ˌpizəm
( plural allotropies also allotropisms )
Etymology: all- + -tropy, -tropism
: the phenomenon of the existence of a substance, especially an element, in two or more different modifications usually in the same phase (as different crystalline forms of carbon, iron, and phosphorus or as different kinds of molecules of oxygen and ozone) — compare polymorphism