I need it for a school project
Polymorphs is a term used to indicate when a chemical compound can exist in different crystal forms. Same compound, different crystal structure. The polymorphs are not really of quartz, because quartz is defined by a particular structure (has a specific arrangement of atoms in three dimensions). The polymorphs are of SiO2: SiO2 (silica) can exist as quartz or as other minerals having precisely the same chemical composition but a different crystalline structure. A polymorph is actually a different mineral. Pyrite is not marcasite; calcite is not aragonite; Quartz is not cristobalite. The main reason that a compound will have polymorphs is that there are several different arrangements that the components can arrange themselves, and with polymorphs, there is not a major difference in energy of any of the possible arrangements. Strictly speaking, any compound could conceivably fit into any of the possible crystal forms but simply does not because those alternative forms are not energetically stable; if they accidentally fall into such a structure, they pretty well immediately jump back out of it. Polymorphs tend to be similar in energy state to their alternatives. Which one gets favored by nature varies according to conditions.
