Inside a mineral, atoms arrange themselves into a specific, repeating pattern called a crystal lattice or crystal structure. The smallest three-dimensional arrangement within the lattice is called a "unit cell," which is duplicated over and over again symmetrically. At the level of the everyday world, minerals that are growing without outside interference tend to form crystals that resemble their underlying crystal structures. Scientists call that kind of general, typical appearance a "crystal habit." Of course, conditions that existed during a mineral's formation or crystal growth may change its habit, but geologists still find this attribute to be a useful tool for identifying minerals. Scientists use more than three dozen adjectives to describe crystal habits. For example, natrolite and rutile can be acicular, or needlelike; quartz often forms hexagonal prisms; pyrite and halite typically crystallize as cubes; and mica is foliated or lamellar (layered).

Ores are rocks that contain minerals rich in elements that are valuable to human society. Almost all the metals we use - iron, aluminum, lead, copper, zinc, uranium, and others - come from ores. To form ores, elements and compounds must be concentrated via one of several processes. In hydrothermal processes, hot water seeping through the ground may concentrate metal-rich minerals into veins. Dense minerals from which we get metals such as platinum, nickel, and chromium crystallize and settle out of some types of magma (molten rock) underground. Much of the iron we use comes from banded iron formations: rock built up from layers of sediments containing iron oxides. Other minerals become concentrated through erosion, transport, and deposition of small rock grains. Mining began in ancient Egypt, Greece, and Rome, followed by a steady stream of technological improvements during the medieval and early modern eras. Today miners use specialized heavy equipment for both surface and underground mining.