The 4,000 or so minerals found in Earth's crust serve as the building blocks of rocks. Ever since humans began fashioning tools out of stone, minerals have played an important role in technology. Televisions, toasters, and toothpaste all contain naturally occurring inorganic and crystalline substances called minerals. Hardness, color, and specific gravity (a measure of density) are some of the more common criteria that influence which minerals get used in making such items as cutting tools, paints, and high-performance tennis rackets.

Gems are particularly valuable minerals because of their beauty and rarity. Rubies, emeralds, and diamonds are among the most precious of mineral gems. But more abundant minerals also have value. If a mineral can be extracted for a profit, it is called an ore. Examples of ores are iron (found in hematite), aluminum (found in bauxite), and copper (found in basaltic lavas).

Mining is the extraction of ores or other rock materials from the Earth either at or near its surface (surface mining) or deeper underground (subsurface mining). Open-pit mining, one form of surface mining, is used where the surface material covering the deposit is relatively thin or else structurally unsuitable for tunneling. Open-pit mines are found in sandy or gravelly terrain. Bauxite and hematite are extracted using surface mining techniques.

Subsurface mining techniques include strip mining, in which deep layers of soil and rock that lie on top of a mineral deposit are removed before specialized machines come in to extract the mineral. Huge amounts of material may be removed — sometimes to tens of meters (more than 30 feet) deep — leaving gaping holes in the Earth. When an ore-producing vein — a mineral-filled crack in rock — runs underground, tunneling may be required to follow it. Shaft mining, which is often associated with coal mining, involves such tunneling. Lifts or conveyor belts remove material from these tunnels for processing.

Modern mining companies in many countries are required by law to return mined land to its original state. This is because many environmental and health hazards are associated with mining waste. For example, rainwater that seeps through mining waste may contaminate ground water with toxic metals such as lead. Where government regulation or enforcement is weak, these hazards can plague local populations and the environment.

Print Background Essay