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.