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Tholeiitic Basalt

Two major groups of basalts are generally scientifically recognized: tholeiitic basalts and alkali olivine basalts. Tholeiitic basalts are formed from magmas of the same name, which produced the mid-ocean ridge basalt and built the Hawaiian Islands, Iceland, and other mid-oceanic landmasses. This type of basalt is present on Earth in much greater amounts than alkali olivine basalt, which occurs along continental rifts and on oceanic islands. The dominant materials that comprise tholeiitic basalt are plagioclase feldspar, clinopyroxene, and iron ore. Unlike alkali olivine basalts, the fine-grained tholeiites contain little or no olivine


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