Both rocks and minerals are naturally occurring substances.
Rocks and minerals can both reveal important information about the history of Earth. Both are hard solids that have been subjected to the elements for thousands of years. The key difference between rocks and minerals is that minerals create rocks, while rocks are homogenous solids. This results in several interesting differences between the composition and appearance of rocks and minerals.
Gold is both a chemical element and a mineral.
Elements are substances that consist of only one type of atom. Minerals are made of either single elements or combinations of elements. Solid gold, for example, is a mineral made of one element. Calcium, conversely, is a compound of calcium and carbon. Rocks contain more than one mineral.
Granite is composed of feldspar, quartz and mica.
Rocks and minerals can be differentiated based on shape. Minerals usually have a definite shape. For example, a mineral may be formed entirely of crystals. Rocks, conversely, may have different shapes at different points. The top of a rock may be crystallized while the bottom may be flat and matte. Granite is a rock made from several minerals, which is why a single piece of granite does not have a uniform shape.
This rock contains quartz and does not have a uniform color.
Minerals typically have a uniform color. Quartz is a mineral, and a piece of quartz will be one color. A rock made from quartz, however, may be different colors throughout.
This rock is covered in fossils.
Rocks can be altered by erosion, wind and heat. Though minerals can be destroyed or changed into rock by environmental factors, they can’t be turned into different minerals. The result is that rocks often have fossils in them. Minerals do not contain fossils. When minerals combine with other minerals they can be fossilized, but are no longer minerals.
Limestone is made of calcium and carbon.
In order to judge whether something is a rock or mineral, it’s helpful to know some common examples of each. Common minerals include mercury, opal, quartz, iron and zinc. When minerals combine to form rocks they can create common rocks like granite, limestone, sandstone and shale.