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Article: Pillow basalt.(Word to the Wise)(Editorial)
- Article from:
- Rocks & Minerals
- Article date:
- July 1, 2005
- Author:
CopyrightCOPYRIGHT 2005 Heldref Publications. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Basalt is a fine-grained igneous rock that is primarily composed of the iron- and magnesium-rich minerals pyroxene and olivine and calcium-rich plagioclase feldspar. It forms from the rapid cooling of mafic (Si[O.sub.2] concentration between 48 and 52 wt. %) magma. When basaltic magma is extruded slowly into water (picture extrusion of toothpaste from a tube), a chilled rind will form on all sides of the extrusion. The hot rind is solid but elastic (like a balloon), and continuous injection of lava into it leads to bulbous, spherical, or tubular lobes that eventually solidify to form pillow-shaped masses of basalt. Not surprisingly these masses are called pillow basalts, ...
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