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Snakestone or Serpentinite http://csmres.jmu.edu/ Serpentine minerals (magnesium silicates; (Mg, Fe)3Si2O5(OH)4). Olive-green, blackish to yellowish green, greasy, waxy, or silky minerals with a hardness of 3-5. ... http://geology.about.com/ Serpentinite is California's state rock. This 1-1/2 meter serpentinite boulder sits in a place of honor in the roof garden of the Oakland Museum of California, its polished surface gleaming blue and jade-green. This rock is composed almost exclusively of minerals of the serpentine group, which forms from the alteration of oceanic mantle rocks. (See more about serpentinization and its importance in plate tectonics.) It happens that northern California's Coast Ranges are full of just that kind of material, carried by plate motions against the North American plate and obducted onto the continent, where the delicate rock type is preserved. ... . http://en.wikipedia.org Serpentinite is a metamorphic rock comprised of an admixture of serpentine minerals. Minerals in this group are formed by serpentinization, a metamorphic chemical alteration of the Earth's mantle occurring at the sea floor at tectonic plate boundaries. It is the state rock of California, USA....Serpentinization is a geological metamorphic process involving heat and water in which low-silica mafic and ultramafic rocks are oxidized and hydrolyzed with water into serpentinite. The peridotites and dunites of the seafloor are converted to serpentine and magnetite. In the process large amounts of water are absorbed into the rock increasing the volume and destroying the structure. The density changes from 3.3 to 2.7 g/cm3 with a concurrent volume increase of about 40%. The reaction is exothermic and large amounts of heat energy are produced in the process.... http://vulcan.wr.usgs.gov/ Serpentine: A family of silicate minerals rich in magnesium and water, derived from low-temperature alteration or metamorphism of the minerals in ultramafic rocks (intrusive igneous rocks very rich in iron and magnesium and with much less silicon and aluminum than most crustal rocks, most come from the Earth's mantle). Serpentine minerals are light to dark green, commonly varied in hue, and greasy looking; the mineral feels slippery. Serpentinite: Rocks made up of serpentine minerals are called serpentinite. ... |
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