# Average Composition of the Continental Crust Weight PercentVolume Percent Si O O Table 3.4.

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Average Composition of the Continental Crust Weight PercentVolume Percent Si O O Table 3.4

Olivine: formed from single silica tetrahedra

Phase – olivine ; Mg 2 SiO 4 Components: Mg(2), Si, O(4) Can be reduced to MgO(2) and SiO 2 Which is 66.67 mole percent MgO and 33.33 mole percent SiO 2 This can be converted to weight by:.6667 moles MgO X 40.31g/mole = 26.875g.3333 moles SiO 2 X 60.09g/mole = 20.028g 46.903g Giving 57.3 weight % MgO and 42.7 weight % SiO 2

Given: 57.3 wt.% MgO and 42.7 wt.% SiO 2 57.3g / 40.31g/mole = 1.4215 moles MgO 42.7g / 60.09g/mole = 0.7106 moles SiO 2 1.4215/(1.4215 + 0.7106) x 100 = 66.67 mole % MgO 0.7106/(1.4215 + 0.7106) x 100 = 33.33 mole % SiO 2 Or a mole ratio ( sometimes called “atomic”) of 2 MgO to 1 SiO 2 The mineral formula would then be based on 4 oxygens giving Mg 2 SiO 4, which is olivine ( specifically forsterite)

Actual analysis (wt.) would give 34.5 % Mg, 20.0 % Si (with the remaining 45.5 % assumed to be oxygen) Mg (24.31g/mole), Si (28.09g/mole) O ( 16.00g/mole) 34.5g / 24.31g/mole = 1.42 moles 20.0g / 28.09 g/mole = 0.71 moles 45.5g / 16 g/mole = 2.84 moles Mg 1.42 Si 0.71 O 2.84 converted to 1 mole O gives Mg 0.5 Si 0.25 O 1 converted to whole numbers gives Mg 2 Si O 4

Classification of Igneous Rocks Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall. Rock with 70% X, 20% Y, 10% Z Plot mineral composition of triangle diagram

Classification of Igneous Rocks (c) Mafic rocks: plag, pyroxene, olivine Norite: gabbro with more opx than cpx Top and bottom fields at 10% tick marks Side fields at 5% tick marks

G225 – Review For Exam 1 Models of the atom Rutherford, Bohr, deBroglie Electronic configuration Quantum numbers Periodic Table Valence electrons ; oxidation- reduction Z and A numbers Isotopes ; stable and radiogenic Bonding Ionic Covalent VanderWaals Metallic Polar versus non-polar Electronegativity Atomic structures Ionic radii – bond lengths

Coordination numbers Hexagonal and cubic closest packing Pauling’s Rules Radicals Isodesmic, anisodesmic, mesodesmic Silicate tetrahedral linkages; subclasses; polymerization Mineral compositions and plotting procedures; solid solution

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