Orthosilicates - Orthosilicates Isolated tetrahedron; Si/O...

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Orthosilicates • Isolated tetrahedron; Si/O ratio ¼; not polymerized • Common orthosilicates: - Olivine, garnet, and zircon: all oxygen in silica tetrahedron - Al 2 SiO 5 polymorphs, staurolite, topaz, titanite: oxygen coordinate with other anions Olivine Group • Structure: - octahedrons occupied with Fe 2+ , Ca 2+ , Mg 2+ - Two distinct sites: M1 and M2 - M1 are stretched out along c axis - M2 less distorted - distortion decreases symmetry – orthorhombic - crystals can be elongate along c axis • Composition - complete solid solution between Forsterite and Fayalite - Mn end member as well, but rare - Fe and Mg contents cause variations in physical properties - Can be used to identify composition - Zoning can be common • Occurrence - common mafic and ultramafic mineral - mantle - metamorphosed carbonate rocks 1
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• Important factoid: - Olivine unstable at high pressure of mantle - convert to more dense phase (~6% more dense) - very similar to spinel structure (a metal oxide) - At 400 km depth, seismic velocity increases (greater density0
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This note was uploaded on 07/06/2011 for the course GLY 5245 taught by Professor Staff during the Spring '11 term at University of Florida.

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Orthosilicates - Orthosilicates Isolated tetrahedron; Si/O...

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