Synthetic equivalents of some minerals, such as emeralds and diamonds, are often produced in the laboratory for experimental or commercial purposes. The composition of a mineral can be defined by its chemical formula. The identity of its anionic group determines the group into which the mineral is classified. A mineral crystallizes in an orderly, three-dimensional geometric form, so that it is considered to be a crystalline material. Along with its chemical composition, the crystalline structure of a mineral helps determine such physical properties as hardness, color, and cleavage.
Minerals combine with each other to form rocks.
For example, granite consists of the minerals feldspar, quartz, mica, and amphibole in varying ratios. Rocks are thus distinguished from minerals by their heterogeneous composition. A mere 100 of the several thousand known types of minerals constitute the main components of rocks. Learn about crystal structures by viewing an interactive movie. Approximately 3,000 minerals exist in nature.