The primary source material from which the Earth’s crust is constructed is the volcanic and plutonic rock of the spreading centres of the ocean basins. The primary magnetic minerals of the crust are the minerals of such rocks. Just as the rocks are altered in the submarine environment, reworked at the subduction zones, weathered and eroded as continental igneous rocks, deposited as sediments, metamorphosed, eroded and so on, so do the magnetic minerals undergo a long and complicated history over geological time. The magnetic minerals are compounds of iron, this being the most abundant of the transition elements. The iron of the primary rocks is distributed between both magnetic and non-magnetic phases. In the course of geological time, the iron of the primary magnetic phases may come to be contained in non-magnetic phases and vice versa. These transformations may occur many times over in the course of alteration, solution, precipitation and metamorphism.
KeywordsOctahedral Site Spinel Structure Magnetic Mineral Cation Distribution Hexagonal Unit Cell
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