What is defined as a naturally occurring, inorganic solid with a specific composition and crystalline structure?

The definition provided refers specifically to a mineral. Minerals are classified as naturally occurring, meaning they form through natural geological processes without human intervention. They are inorganic, which means they do not originate from living organisms.

Furthermore, minerals have a specific composition, which indicates that they are made up of particular elements in a defined proportion, and they possess a crystalline structure, which gives them a regular repeating arrangement of atoms. This crystalline structure is a key characteristic that distinguishes minerals from other natural substances.

When considering the other options, gems are often polished or cut versions of minerals but do not encapsulate the entire definition of a mineral. An element is a pure substance consisting of only one type of atom and does not necessarily have a crystalline structure. Compounds consist of two or more elements chemically bonded together, and while they can be minerals if they are in solid form and have a crystalline structure, the term "mineral" is more specific in this context. Thus, the correct choice aligns perfectly with the mineral definition.