Rocks are made of Minerals.
Minerals are chemicals found in nature. Minerals are formed by inorganic processes not by living things.
Each mineral has the same structure and composition. They also have the same physical and chemical properties.
Some minerals like feldspar do not have an exact chemical composition. Instead they are a family of closely
related chemical compounds. Most minerals are found in crystalline form. Table Salt is a mineral.
Rocks can be made of a single mineral like Quartz Crystals or Gold.
But most rocks are made of mixtures of minerals cemented together. Granite and Basalt are the
most common examples.
Dictionary Definitions taken from The Readers Digest Great Encyclodepic Dictionary.