Mineral (n.) – an inorganic, naturally-occurring crystalline solid with a definite, but not necessarily fixed, chemical composition and crystal structure. Formation of minerals occurs as a precipitate from a solution, as the result of high temperature and pressure within a preexisting rock, or from the cooling of molten rock. Minerals are important because they are the building blocks of earth’s crust, are helpful in understanding the formation of the earth, and are essential in engineering.
Minerals are classified based on the principal anion or anionic group within their chemical structure. The main classes of minerals are:
- Silicates (e.g. quartz, feldspar, olivine)
- Oxides (e.g. hematite, magnetite, corundum, ilmenite, rutile)
- Sulfides (e.g. galena, pyrite, chalcopyrite, sphalerite)
- Sulfates (e.g. gypsum, barite, anhydrite)
- Halides (e.g. halite, fluorite)
- Carbonates (e.g. calcite, dolomite, aragonite, siderite)
- Native metals (e.g. gold, copper)
Silicate minerals comprise over 90% of Earth’s crust and have their own classification system based on their crystal structure. There are five different possible structures and each have a variety of silicate minerals that exhibit that structure.
- Isolated tetrahedra: olivines, garnets, zircon, andalusite, kyanite, sillimanite
- Single chain: pyroxene, diopside, jadeite
- Double chain: amphiboles
- Sheet silicates: biotite, muscovite, clay minerals, serpentine
- Framework silicates: quartz, feldspars
There is a commonly-accepted group of rock-forming minerals for each type of rock, primarily due to their formation and growth.
- Igneous rocks are mainly composed of feldspars, muscovite, biotite, quartz, amphibole, pyroxene, and olivine
- Sedimentary rocks are mainly composed of quartz, clay minerals, and calcite
- Metamorphic rocks have inclusions of garnet, kyanite, sillimanite, staurolite, andalusite, chlorite, and epidote