Mineral resources: the minerals extracted from the earth"s upper crust for practical purposes. Metals: a solid composed almost entirely of atoms of metallic elements; it is generally opaque, shiny, smooth, malleable, and can conduct electricity. Native metals: a naturally occurring pure mass of a single metal in an ore deposit. Smelting: the heating of a metal-containing rock to high temperatures in a fire so that the rock will decompose to yield metal plus a nonmetallic residue (slag) Alloy: a metal containing more than one type of metal atom. Precious metals: metals (like gold, silver, and platinum) that have high values. Base metals: metals that are mined but not considered precious. Ore: rock containing native metals or a concentrated accumulation of ore minerals. Ore minerals: minerals that have metal in high concentrations and in a form that can be easily extracted. Ore deposit: an economically significant accumulation of ore.