Rocks are composed of minerals, which are naturally occurring, inorganic solids with a definite chemical composition and crystal structure. Minerals are the basic building blocks of rocks and can be identified by their physical and chemical properties, such as color, hardness, luster, and crystal form.

Mineraloids

Mineraloids are naturally occurring, inorganic solids that do not have a definite chemical composition or crystal structure. They are similar to minerals, but they do not meet all of the criteria to be considered true minerals. Some common mineraloids include opal, obsidian, and tektite.

Organic matter

Rocks can also contain organic matter, which is the remains of living organisms. Organic matter can include things like plant debris, animal bones, and shells.

Other materials

In addition to minerals, mineraloids, and organic matter, rocks can also contain other materials, such as water, air, and volcanic ash.