Lead comes from natural sources in the Earth's crust, primarily from lead- containing minerals, especially the mineral galena (lead sulfide, PbS), which is the main ore used to extract lead. These lead minerals originally formed from volcanic flows from the Earth's mantle, and natural processes have concentrated lead into economically significant deposits around the world, including in the United States, Canada, Australia, and several other countries. Lead is rarely found free in nature and is usually extracted from ores by roasting and smelting processes. Cosmically, lead was created mainly by neutron capture processes in stars, and it has accumulated in the Earth's crust over billions of years. It is a soft, blue-gray metal that has been used since antiquity for various purposes including water pipes by the Romans, and today it is mostly used in car batteries. Lead can also be found in the environment due to human activities such as mining, smelting, industrial processes, and past use in leaded gasoline, paint, plumbing, and other products. Exposure to lead commonly occurs through these routes, especially when lead-containing materials deteriorate or contaminate soil, water, or air.