What is a fundamental characteristic of a mineral?

A fundamental characteristic of a mineral is that it is not a rock. Minerals are naturally occurring, inorganic substances with a specific chemical composition and crystalline structure, while rocks are aggregates made up of one or more minerals. This distinction is foundational in geology as it helps categorize materials found in nature.

The other choices are not characteristics of minerals. Minerals are solid, not liquid or gas, and they are formed through natural geological processes rather than being artificial. Being composed solely of gas does not apply to minerals, as minerals must have a solid crystalline structure.