Minerals and rocks

A mineral is a obviously occurring, inorganic solid with a definite chemical composition and a crystalline structure. A rock is an collective of one or more minerals. (A rock may also include organic remains and mineraloids.) Some rocks are mostly composed of just one mineral. For example, limestone is a sedimentary rock composed almost wholly of the mineral calcite. Other rocks have many minerals, and the specific minerals in a rock can vary widely. Some minerals, like quartz, mica or feldspar are general, while others have been found in only one or two locations worldwide. The vast majority of the rocks of the Earth's crust consist of quartz, feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals.Over half of the mineral species identified are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains.
Commercially costly minerals and rocks are referred to as industrial minerals. Rocks from which minerals are mined for economic purposes are referred to as ores (the rocks and minerals that remain, after the desired mineral has been separated from the ore, are referred to as tailings).