What is the term for a natural substance that has a defined chemical composition and crystalline structure?

The correct term for a natural substance that has a defined chemical composition and crystalline structure is mineral. Minerals are naturally occurring inorganic solids that have a specific chemical formula and a crystal lattice structure, which gives them distinct properties such as hardness, color, and luster. This definition encompasses the key aspects of minerals, including their natural origin and organized atomic arrangement.

In contrast, rocks are aggregates of one or more minerals or mineraloids, meaning they do not have a uniform chemical composition or crystalline structure themselves. Soil is a complex mixture composed of minerals, organic matter, water, and air, and it does not meet the criteria of having a defined chemical composition and crystalline structure. Elements are pure substances consisting of only one type of atom and do not possess the crystalline structure characteristic of minerals.