The document discusses the composition and characteristics of minerals that make up the Earth's crust. Minerals are naturally occurring substances composed of elements and ions bonded together. They are solid, inorganic compounds with defined chemical compositions. Common minerals include quartz, feldspar, calcite, and many others. Minerals can be classified based on their chemical makeup and physical properties such as color, hardness, crystal structure, and streak. Together minerals constitute the solid rocky materials that form the Earth's crust.