Test 1 Minerals Know the eight most abundant elements in the Earth s crust their most common ionic form relative ionic sizes and the most common coordination numbers of these ions Ion is a charged atom Cations have a positive charge Anions have a negative charge Coordination number is the number of atoms or ions immediately surrounding a crntal atom in a complex or crystal most abundant elements in Earth s crust Ionic Sizes Coordination Number element O oxygen Si silicon Al aluminum Fe iron Ca calcium Na sodium K potassium Mg magnesium O 2 Si 4 Al 3 Fe 2 Ca 2 Na 1 K 1 Mg 2 Only anion 4 4 or 6 6 8 8 8 12 6 The distinction between crystalline and non crystalline solids Crystalline solids exhibit cleavage that is when you break them the nature of the break indicates the crystal structure Non Crystalline solids such as glass break into randomly shaped pieces exhibiting no cleavage The most common silicate minerals olivine pyroxenes amphiboles biotite muscovite plagioclase feldspar alkali feldspars quartz Olivine Mg Fe Si O independent tetrahedral Pyroxenes Mg Fe Si2 O single chain Amphiboles W X Al Z O double chains Biotite mica K Mg Fe Al Si3 O sheet silicates Muscovite mica K Al Si3 O sheet silicates Alkali feldspars K Al Si3 O Na Si3 framework silicates Plagioclase feldspars Na Al Si3 Ca Si2 framework silicates Quartz Si O framework silicates Atomic or ionic substitution in silicates factors controlling substitution commonly substituting ion pairs and degree of substitution W represents the large cations Ca Na and K that can substitue for one another X represents the smaller Mg and Fe Z represents the cations in the tetrahedral sites Si and Al Relationship of cleavage to structure in silicate minerals Cleavage is the splitting or tendency to split of a crystallized substance along definite crystalline planes yielding smooth surfaces Meaning of mafic felsic Mafic A term used to describe an igneous rock that has a large percentage of dark colored minerals such as amphibole pyroxene and olivine Felsic A term used to describe an igneous rock that has a large percentage of light colored minerals such as quartz feldspar and muscovite How heat is transferred radiation conduction convection Earth s Heat Radiation heat moves as electromagnetic radiation such as heat transferred from the Sun to Earth Conduction enhanced vibrational motion of atoms in materials is induced in neighboring atoms and this motion diffuses through the material if you could actually see the atoms a very crude analogy might be a crowd in a football stadium doing the Wave Convection heat is carried by matter which is flowing Warmer and less dense matter rises while cooler and denser matter sinks Sources or origins of the Earth s Heat Kinetic energy from the intense bombardment of the earth by meteorites throughout earth s history is transferred through shock waves that compress rock Ultimately all motion must cease and the results are that kinetic energy is converted to thermal energy and the planet heats up a bit SUMMARY COPY PASTED During the early history of the solar system the Earth and other planets grew in size and mass as comets asteroids and other smaller masses fell into them This process continues today albeit at a much slower rate Today meteorites that reach Earth have velocities of approximately 30 70 km sec Large ones therefore posses considerable kinetic energy kinetic energy mass x velocity2 As they strike Earth their velocity and thus their kinetic energy drops to zero A fundamental principle of physics consevation of mass energy tells us that the kinetic energy must be conserved in some form Most likely two things happen to this energy Some of it is initially spent doing mechanical work such as compressing the atmosphere through which it travels a small fraction producing shock waves that compress rock and breaking and moving rocks around craters a large fraction Ultimately all motion the shock wave and rocks must cease and the result is that kinetic energy is converted to thermal energy which means that the motion is transferred to the atomic scale and the planet heats up a bit Under the intense bombardment of the Earth during its earliest history the planet s temperature must have risen significantly perhaps to the point where some part of the planet melted Since that early history the Earth has been cooling but some of that original heat remains The geothermal gradient and geobarometric gradient Geothermal Gradient The rate at which the temperature increases with depth in the Earth Geo Barometric Gradient Also called a Pressure Gradient The change in atmospheric pressure per unit of horizontal distance in the direction in which pressure changes most rapidly Magmas Melting of silicate rocks effects of temperature pressure and water how composition of magmas are influenced by the degree of partial melting of source rock The temperature required to melt minerals increase with increasing pressure Rocks within the earth s interior for example are so hot but because of the pressure they stay solid If the pressure was to be released or they were moved into a lower pressure zone the rock would melt Temperature Difference silicate rocks melt at different temperatures Pressure An increase in pressure means that the melting point of the silicate rock increases Water and Volatiles Rocks containing water melt at lower temperature then that of dry rocks contraining identical mineral assemblages Magmas Cooling magmas crystallize assemblages of minerals referring to as igneous rocks which the dominate mineral is silicates A slow cooling rate provides time for crystals to develop while raid cooling does not Magma deep within earth form crystals due to pressure because of the difficultness of losing heat Magmas closer to the surface or enclosed in cool rocks can produce smaller crystals and magmas erupting onto the surface of the earth cool so quickly it hardens before it has a chance to produce crystals Role of pressure and volatiles water and gases on melting See pressure above and water above Factors influencing the viscosity of magmas Heating reduces viscosity The viscosity increases with increasing silica content due to silica chains Low viscosity fluids slow more easily than high viscosity fluids Crystallization of magmas mineral sequence with decreasing temperature equilibrium vs fractional crystallization mechanisms and effects on the composition of magmas Crystallization of magmas depends on the
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