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The iron of the Mesabi
The Mesabi Range in Minnesota is a ridge of iron-bearing rock, formed on a sea floor around 1.9 billion years ago. The Mesabi Range supplied the bulk of the iron ore for American steel from the 1890s and through both world wars. The connection is worth registering: a biological event in the Precambrian determined where twentieth-century industrial power could be built. The richest haematite ores were exhausted by about 1950, and the industry moved to taconite, a leaner rock that has to be concentrated.
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