Coal is the most abundant source of electricity worldwide, currently providing more than 36% of global electricity. Coal also serves many industrial uses. Among the most significant are steel production, which uses metallurgical/coking coal, and cement manufacture. Coal and coal by-products are also used to manufacture a variety of goods, including activated carbon used in filters for water and air purification systems; carbon fiber in the construction of airplanes and automobiles; silicon metal for lubricants and even chemical processes to extract rare earth elements etc.