Metals often appear in the Earth's crust as an ore. An ore is the metal usually in the form of a compound, most commonly an oxide. When the ore is dug up, and decomposed to the metal alone, we call this extracting. The more reactive a metal the more difficult to extract. Unreactive metals, such as gold and silver can be found as pure elements in the Earth's crust. There are different methods of extraction: Electrolysis. Heating with carbon monoxide. Roasting in air. Metals are a non-renewable resource. Hence, it is important to recycle used metals. Aluminium is extracted from the ore bauxite, using electrolysis. At the cathode, aluminium is formed and at the anode oxygen gas forms. Aluminium has many useful properties: Shiny. Good conductor of heat and electricity. Malleable and ductile. Low density. Iron is extracted from the ore haematite (iron oxide) using a blast furnace. Cast iron and steel are two useful by-products from the extraction of iron. The corrosion of iron and steel is called rusting. Rusting of iron occurs if both water and oxygen (usually from the air) is present. To help prevent rust, several methods may be used: Paint or grease. Galvanising. Sacrificial protection.