Lecture 6 Minerals and SilicatesQuestions to ponder:Complex Ions (radicals) The silica-oxygen tetrahedral SiO4PowerPoint PresentationSlide 5/’’’’’’’’’’The SiO4 Tetrahedral can be represented in many ways:Because the SiO4 still has a 4- charge, it can bond to other silica tetrahedrals, and a variety of CationsSlide 9Slide 10Various Cations can bond with silicatesSometimes various cations may substitute for one anotherSlide 13Rock-Forming MineralsFerromag Minerals MAFICSlide 16Sialic Minerals FELSICSlide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Igneous RocksIgneous Rocks –TextureSlide 30Slide 31Slide 32Igneous Rocks – CompositionName change between Mineral composition and Magma/Rock compositionSlide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slow cooling – Intrusive (plutonic)Slide 43Rapid cooling – Extrusive (volcanic)Slide 45Lecture 6Minerals and SilicatesQuestions to ponder:•Why is the silicate tetrahedral so important?•What forms does the silica tetrahedra; form when bonding to other silica ions?•What is Felsic mineral? Mafic mineral?Complex Ions (radicals)The silica-oxygen tetrahedralSiO4Silicate minerals7. SilicatesSilicates: Cations combine with a unit that consists of 1 silicon and 4 oxygen ions (SiO4)-4Quartz (SiO2)Collectively, silicates comprise about 1/3 of all mineral speciesSilicate minerals account for about 95% of the volume of the Earth’s crust and are the “Rock-forming” mineralsTogether, oxygen (O) and silicon (Si) make up about 75% of the Earth’s crust/’’’’’’’’’’The basic building block of all silicate minerals is the silicon-oxygen tetrahedron4 oxygen ions, each with a valence of -2 (4 X –2 = -8)The structure of the (SiO4)-4 unit is a function of the radii (or size) of the ions1 silicon ion, with a valence of +4 (1 X +4 = +4)-4The SiO4 Tetrahedral can be represented in many ways:Imagine a tennis ball surrounded by 4 volleyballsBecause the SiO4 still has a 4- charge, it can bond to other silica tetrahedrals, and a variety of Cations(Also called 3D structure)Various Cations can bond with silicatesSometimes various cations may substitute for one anotherSi and Al are about the same size, but have different charges(SiO4) -4 and (AlO4) -5This adds variety and complexity to the potential for mineral formsTypes of 3-D silicate mineralsFeldsparPlagioclase Orthoclase (NaAlSi3O8 (KAlSi3O8) CaAl2Si2O8)Rock-Forming Minerals•About 20 common minerals make up most rocks–Silicates dominate–Quartz, Feldspars, Mica, Amphiboles, Pyroxenes•Silicates can also be subdivided by composition–Ferromagnesium – High in Iron and Magnesium–Sialic – High in Silica and AluminumFerromag MineralsMAFIC•Silicate minerals rich in iron and magnesium–Relatively high density and higher crystallization temperatures–Olivine – Isolated SiO4 Tetrahedra–Pyroxenes – Single Chains–Amphiboles – Double Chains–Mica – biotite – Sheet silicatesSialic MineralsFELSIC•Silicate minerals rich in silicon and aluminum–Relatively low densities and low crystallization temperatures–Quartz – Framework Silicates–Feldspars - Framework Silicates•Potassium feldspar•Plagioclase feldspar–Mica – muscovite – Sheet silicatesSialic MineralsMinerals•“Naturally occurring, inorganic solid with a specific chemical formula and definite crystal structure”•The crystal structure and the elements involved indicate much about the conditions in which a mineral formed•Silicate minerals (SiO4), comprise about 95 % of earth materialMinerals and Temperature•Non-silicate minerals, in general, form at lower temperature and pressure conditions than do silicate minerals–Oxides, Halides, Hydroxides, Carbonates, Sulfates, etc•Ferromag silicate minerals form at higher temperatures than do Sialic minerals–Ferromags – high in Fe and Mg (as well as Ca)–Sialic – high in Si, Al and O, little or no Fe, Mg, CaRocks = Aggregates of minerals•Therefore, minerals provide clues as to how the rocks may have formed–What parts of earth do you expect lower Pressures and Temperature? Where would you expect to find Higher P and T?•Further, the presence or absence of certain minerals may also indicate the processes that have acted upon our rocks, over time•How minerals are arranged in rocks (their relationship to one another) also provides insight towards the rock-forming processes•Rocks are classified by: 1) Texture – the size, shape and arrangement of crystals, and 2) Composition (mineralogy)Example of a rock and the mineral composition + texture3 Main Categories of RocksEach category will be further subdivided•IgneousIgneous – new rocks being made–Form from crystallizing magma/lava–High temperature minerals•SedimentarySedimentary – weathering of pre-existing rocks–Form from weathering, erosion and deposition of sediments and minerals–Chemical precipitates (Abiotic and biotic)–Lower temperature minerals•MetamorphicMetamorphic – alteration of pre-existing rocks–Form from combinations of Heat, Pressure, + Fluids–High T and/or P minerals–Recrystallize, but DO NOT melt!The role of Plate Tectonics to Rock formationIgneous RocksRock CycleTemperatureAnd PressureIgneous Rocks•“From Fire”•Crystallization of Magma/Lava•2 subcategories (with further subdivision)–Extrusive (Volcanic)•Lava at or very near the earth’s surface–Intrusive (Plutonic)•Magma at depth in earth’s crust•Silicate minerals dominate; some oxidesIgneous Rocks –Texture•Texture – size, shape and arrangement of minerals•Igneous rocks > Interlocking crystals•Size of the crystals help us make the first division of Igneous Rocks•Crystal size determined by cooling rates of magmaExtrusive (Volcanic)Intrusive (Plutonic)The Nature of Igneous Rocks•Form from Magma–Hot, partially molten mixture of solid liquid and gas–Mineral crystals form in the magma making a crystal “slush”–Gases - H2O, CO2, etc. - are dissolved in the magma–Magma is less dense than solid rockThe Nature of Igneous Rocks•Magma vs. Lava–Magma is molten rock beneath the surface–Lava is molten rock that has reached the surface–Magma solidifies to form intrusive igneous rocks–Lava solidifies to form extrusive igneous rocksIgneous Rocks – Composition•Composition = the mineralogy of the magma and hence, rocks•While texture allows us to separate