Steel is iron that has most of its impurities or flaws removed to make it stronger and more durable. Starting in 1856, steel workers turned iron into steel in pearshaped Bessemer converters. In the 1900s, the Bessemer process began to be replaced with the open hearth process. Both of these methods required a large amount of natural resources. The Midwest was abundant with all of the nessecary materials to create steel. This made the Great Lakes region an ideal location to setup steel industries. Coal, oil, iron ore, and limestone were materials needed to create steel. All of these resources were not only in the Midwest, but they were quite abundant. Iron ore was mainly found around Lake Superior where it was abundant. Limestone was scattered in the Midwest, but was mainly found in Northern Michigan. Coal was located in Illinois, Michigan, West Virginia, Ohio, and Pennsylvania. Other resources not needed to make steel but that helped the steel industry grow were the Great Lakes.