At or near Earth's surface, sedimentary rocks form in two ways: by the accumulation of rock grains or by the formation of a solid from minerals dissolved in water. The fragments that go into making sedimentary rocks can be as big as boulders or as small as clay particles. Over long periods of time, the upper layers of debris compress the lower layers, squeezing out excess water or air trapped between the rock fragments. Under the pressure, individual fragments eventually dissolve and stick together, or the remaining fluid within the sediment brings in other substances that act as a cement, until the sediment has turned into rock. Scientists classify many sedimentary rocks based on the size of the particles that built the rock; mudstone and sandstone, for example, originally came from fine-grained mud and sand deposits that hardened over long time periods.

About 200 years ago, scientists studying electricity realized that metals allowed electrical currents to flow through them much more easily than most nonmetals. Because of its relative abundance, high electrical conductivity, and malleability (or ability to be shaped), copper has become the standard material for electrical wiring and switching. Certain types of low-iron silicates, such as muscovite and pyrophyllite, are naturally occurring electrical insulators. Glass or porcelain insulators, made from such minerals as quartz and feldspar, keep high-voltage power-transmission lines from touching their poles. Pyrolusite is the naturally occurring mineral version of manganese oxide, which is inside every non-rechargeable alkaline battery. Gasoline-powered articles start their engines with a jolt of electricity from lead-acid batteries, which get their lead from the mineral galena. Other rechargeable batteries contain nickel, cadmium, or other metals, found in a variety of ores.