Minerals are naturally occurring, solid substances with a defined chemical composition and a specific, usually crystalline, structure. They are formed by geological processes and are essential components of the Earth's crust.

Here's a breakdown of the key characteristics:

* Naturally Occurring: Minerals are not manufactured or created artificially. They are formed through natural processes within the Earth.

* Solid: Minerals are not liquids or gases at room temperature.

* Defined Chemical Composition: Each mineral has a specific chemical formula that determines its composition. This can be simple, like pure gold (Au), or more complex, like feldspar (KAlSi3O8).

* Crystalline Structure: Atoms in minerals are arranged in a repeating, three-dimensional pattern called a crystal lattice. This gives minerals their specific properties like shape, cleavage, and hardness.

* Inorganic: Minerals are not formed from living organisms. They are derived from geological processes.

Here are some examples of minerals:

* Quartz (SiO2)

* Feldspar (KAlSi3O8, NaAlSi3O8, CaAl2Si2O8)

* Diamond (C)

* Gold (Au)

* Halite (NaCl)

Note: Some materials that are commonly referred to as minerals, such as coal or amber, do not technically meet all the criteria because they are organic in origin.