To meet the definition of “mineral” used by most geologists, a substance must meet five requirements:

naturally occurring  inorganic  solid  definite chemical composition  ordered internal structure

“Naturally occurring” means that people did not make it. Steel is not a mineral because it is an alloy produced by people.

“Inorganic” means that the substance is not made by an organism. Wood and pearls are made by organisms and thus are not minerals.

“Solid” means that it is not a liquid or a gas at standard temperature and pressure. Water is not a mineral because it is a liquid.