Answer:
A well-defined, natural substance with a structure in crystalline form.
Step-by-step explanation:
Minerals have a crystalline structure and are different from elements because they are made of a combination of different elements. For similar reasons they cannot be considered either since rocks do not have a fixed, specific chemical composition and minerals do. As such, the chemical composition defines it as being that particular mineral. Although it must occur in natural form, minerals can have biological or non-biological origins.