One of the most common solids in the universe are the minerals. Minerals are the building blocks of rocks and planets. Although the atomic composition of minerals was generated in stellar furnaces, minerals are not found in stars. By definition, minerals are naturally occurring, inorganic crystalline solids with specific chemical, physical, and optical properties. Minerals can be formed in the laboratory, but must also occur naturally. Minerals do not include the wide group of hydrocarbon-based compounds secreted by biological entities. All minerals have orderly arrangements of atoms in the solid state. Amorphous "solids" (i.e. glasses) lack the degree of atomic organization that characterizes minerals. Glasses are less stable than crystalline matter and naturally occuring glass typically crystallizes over time.

 MINERAL CLASSIFICATION

 The classification of minerals is based on both crystalline structure and elemental composition. Typically, Earth minerals are divided into two major groups: the silicates and the nonsilicates. Most mineral families or groups are named after anionic (i.e. negatively charged) molecules or elements. Mineral species have specific chemical compositions that vary within certain limits.

 TABLE 1. Mineral Etymology (anionic nomenclature)

Minerals on earth are divided into two major categories: silicates and nonsilicates. Silicates comprise the bulk of Earth's crust and mantle. Nonsilicates are concentrated in the inner core and are sparsely, although significantly, disseminated in the crust. Most economic minerals, because of their rarity, are nonsilicates.

Silicates are the most abundant minerals on Earth. All silicates are based upon the silicate tetrahedron (SiO₄), a complex anion that neutralizes its excessive negative charge (i.e. -4) by either ionically bonding with metallic/submetallic cations (e.g. Fe⁺², Mg⁺², Ca⁺², K⁺¹, Na⁺¹) and/or covalently linking with other tetrahedra to form complex structures. Silicate minerals with few tetrahedral linkages are enriched in metallic/submetallic cations, and are consequently silicon-depleted. Silicates with many tetrahedral linkages and are silicon-enriched and are depleted in ionically bonded cations. The most silicon-enriched mineral group, Quartz, has no ionically bonded metallic/submetallic cations and is made entirely of linked tetrahedra.

Silicate minerals are grouped into families based on the crystalline lattice produced by the silicate tetrahedron. Tetrahedra may be solitary, linked tip to tip, linked in chains, linked in linked chains, sheets, or in an anastomosing network. Ionically bonded cations in incompletely linked tetrahedral networks are used for further classification of silicates into families. Silicate species are named for specific compositions and structures.

Because bonds between linked tetrahedra are typically stronger than bonds between tetrahedra and metallic/submetallic cations, cleavage and other physical properties are similar for species in each silicate structural group. Neso- and sorosilicates typically lack cleavage, inosilicates have prismatic cleavage, and phyllosilicates have monodirectional cleavage.

Characteristics used for mineral identification can be classified into three major categories:optical, physical, and chemical. Although many minerals can be classified easily with relativelysimple observations, advanced classification and certain mineral species require additional,specialized study. Common equipment and supplies are required for primary observations. Primaryobservations should be completed for each mineral specimen. Secondary observations should be madefor many mineral species, but are not always necessary. Advanced observations require equipment thatmay be available in many geological laboratories. The following tables list all three types ofobservations.

TABLE 3. Optical properties of minerals: