Antimony ores with mixed sulfides and oxides are smelted in a blast furnace. Carbonate ores are also smelted with charcoal, but sometimes need to be calcined first. Bauxite is refined into alumina, which is later smelted into aluminium. The ore was smelted in Wickes, Montana. Copper concentrates are commonly exported to other countries to be smelted. This situation remained until the early 20th century when no iron ore was being smelted. When iron is smelted from its ore, it contains more carbon than is desirable. It was then smelted in special furnaces made of compacted earth mixed with straw. Primary production is the process by which alumina is smelted to pure aluminum metal. Ore is smelted on site in Norilsk. Nickel ore is smelted at the company's processing site at Norilsk. Hittites did not use smelted iron, but rather meteorites. Many common metals, such as iron, are smelted using carbon as a reducing agent. Mercury has been smelted from cinnabar for thousands of years. The oxides, in turn, are smelted into the metal.