Final answer:
Elements can substitute for each other in mineral structures, resulting in compositional variations within a single mineral. This is known as ionic substitution or solid solution.
Step-by-step explanation:
The subject of this question is Chemistry. Elements can substitute for each other in mineral structures, resulting in compositional variations within a single mineral. This is known as ionic substitution or solid solution.
For example, in the mineral olivine, the composition can vary between magnesium and iron. The chemical formula for olivine is (Mg,Fe)2SiO4, indicating that both magnesium and iron can substitute for each other in the mineral's structure.
So, the correct option is C. Ionic substitution.