Most metals form compounds, called minerals, which are naturally occurring, inorganic solids with regular chemical compositions and crystal structures. Although most metal-bearing mineral compositions comprise several elements, there are a few exceptions such as gold, which is found in its elemental form as a mineral called native gold. Metals can form or be part of many different minerals. The brilliant colours frequently associated with gems such as emerald, ruby and sapphire reflect the variety of metal-containing minerals.
Minerals combine to become the rocks that make up our planet.
Most rocks form considerably below the surface of the earth under the influence of pressure and heat. Geologic processes can cause them to move upward toward the surface. There, in the presence of oxygen and water, they break down, releasing elements including metals into solution, and forming new minerals. This process, known as weathering, forms our soils. From soil, metals are taken up by plants and then by animals and humans in food.