Polymorphism is defined as the ability of a solid material to exist in more than one form or crystal structure, whereas allotropy is defined as the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of these elements. (From wikipedia).
In the case of crystal solids, it seems clear that allotropy is a particular case of polymorphism... but this is always true? That is, both terms, polymorphism and allotropy refer always to crystal structures? Polymorphism definition mentions "crystal structures" but "crystal" does not appears in the definition of allotropy...
Thanks in advance.
UPDATE Thank you for your answer Then, in some cases allotropy is more general than polymorphism. For instance, dioxygen and ozone are allotropes but not polymorphisms. But... my question arises from my TRUE/FALSE set of questions which I have to answer, and one of them is:
In a non-crystal material the concept of allotropy or polymorphism does not exist.
What would you answer to that? My conclusion is that the question is not clear... For polymorphism is true whereas for allotropy it is not.