Dynamic Earth Test One Minerals Eight most abundant elements in the Earth s Crust Most common Ionic Form Fe 2 Ca 2 Oxygen O O 2 Si 4 Silicon Si Al 3 Aluminum Al Iron Fe Calcium Ca Sodium Na Potassium K Magnesiu m Mg K 1 Na 1 Mg 2 Most Common Coordinatio n Numbers Si 4 Al 4 or 6 Fe 6 Ca 8 Na 8 K 8 12 Relative Ionic Size 1 40 0 26 0 39 0 63 1 00 0 99 1 37 0 72 Pneumonic o On o Sunday o Assholes o In o Church o Sing o Pagan o Music The coordination number of a cation is the number of anions that are its closest neighbors i e how many anions are surrounding the cation o Cation Positive charge o Anion Negative charge Oxygen and Silicon are most abundant on earth s crust Their bond is the strongest in minerals Silicon Tetrahedron is the basic building block common to various groups or classes of silicate minerals Distinction between crystalline and non crystalline solids o Crystalline term refers to the ordered symmetrical arrangement of the atoms that make up the structure Minerals are naturally occurring solid chemical compounds with crystalline structure Exhibits cleavage Dynamic Earth Test One o Non Crystalline Ex Glass Soften as the temperature increases and have no sharply defined melting point The Most common silicate minerals Structure and Composition o Olivine Mg Fe 2SiO4 Independent Tetrahedral o Pyroxenes Mg Fe 2Si2O6 Single Chain Amphiboles W X Al 7 8 Z4O11 2 OH 2 double chains W represents the large cations Ca Na and K That can substitute for one another X Represents the smaller Mg and Fe Z Represents the cations in the tetrahedral sites Si and Al o Biotite mica K MgFe 3 AlSi3O10 OH 2 Sheet silicates o Muscovite mica KAl2 AlSi3O10 OH 2 Sheet Silicates o Plagioclase feldspar NaAlSi3O8 CaAl2Si2O8 solid solution series framework silicates o Alkali Feldspars KalSi3O8 CaAl2Si2O8 solid solution series Framework silicates o Quartz SiO2 Framework Silicates Summary o Olivine common independent tetrahedral silicates o Plagioclase common framework silicates o Amphibole common double chain silicates o Pyroxene common single chain silicates o Biotite common sheet silicate o Muscovite mica sheet silicate o Alkali feldspar common framework silicates o Quartz common framework silicate Pairs of elements that commonly substitute for one another in Silicates o Si and Al o Mg and Fe and also Al o Na and K o Na and Ca Factors that control substitution The size of the ions and the size of the crystallographic sites into which they substitute The charges on the ions that are substitution for one another if charges are the same then the crystal structure can remain electrically neutral if charges not the same then other substitutions must take place to maintain charge balance Temperature and pressure at which the substitution takes place Greater amount of substitution takes place at higher temperatures Pressure can change the size of Dynamic Earth Test One both the site and the ion resulting in different substitutions Relationship of Cleavage to Structure in Silicates o Cleavage is the breaking along a planar surface of a silicate and it forms along the planes of ionic bonds Definitions o Mafic silicate minerals magmas and rocks which are relatively high in the heavier elements and rich in magnesium and iron o Felsic silicate minerals magmas and rocks which have a lower percentage of the heavier elements and are correspondingly enriched in the lighter elements such as silicon and oxygen aluminum and potassium While silicate minerals constitute most of the outer part of the solid Earth many other minerals are both geologically and economically important o Native elements o Oxides Gold Silver Copper Magnetite Bauxite Rutile o Sulfides Pyrite Galena o Sulfates Gypsum o Carbonates Calcite Malachite Earth s Heat How is heat transferred Radiation conduction convection o Radiation heat moves as electromagnetic radiation such as heat transferred from the Sun to the Earth o Conduction enhanced vibrational motion of atoms in materials is induced in neighboring atoms and this motion diffuses through the material Like the wave at a game Thermal conduction is very slow o Convection Heat is carried by matter which is flowing Warmer and less dense matter rises while cooler and more dense matter sinks o Silicates are great thermal insulators not conductors Dynamic Earth Test One o Heat flows from warmer bodies to cooler bodies The heat within the planet is being lost to the cooler region of space Original Source of Heat o 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 heating up the earth o Today meteorites that reach Earth have velocities of approximately 30 70 km sec the large ones containing a large amount of kinetic energy that is converted to thermal energy and the planet heats up a bit o Some of the heat can be accounted for by the natural abundance of radioactive elements Uranium Thorium and Potassium Definitions o Geothermal gradient the rate at which the temperature increases with depth in the Earth varies from place to place o Geo Barometric gradient The change in atmospheric pressure per unit of horizontal distance in the direction in which the pressure changes most rapidly Magmas Melting of Silicate Rocks o Magmas form by the melting of pre existing silicate Major mechanisms that can cause a rock to melt are heating pressure decrease addition of water How composition of magmas are influenced by the degree of partial melting of source rock o Partial melting is when only a portion of the parent rock melts always produces a magma that is less mafic than the parent rock way of differentiating material making new rocks that differ in composition from the parent rock Role of pressure and volatiles water and gases on melting o Pressure Temperature required to melt minerals increases with increasing pressure so that minerals which are heated to temperatures sufficient to melt them at atmospheric pressure can remain solid under the high pressure in the Earth Some rock s in the Earth s interior that are solid are so hot that if the pressure on these were released or they are convected into a lower pressure zone they could begin to melt Dynamic Earth Test One o Volatiles The melting temperatures of minerals are reduced under high water pressure Consequently wet rocks rocks containing water melt at lower temperatures that do dry rock containing identical mineral assemblages Factors influencing the
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