GEO 401 Annotated Midterm Study Guide
GEO 401 Annotated Midterm Study Guide GEO 401
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Popular in Geology
This 5 page Study Guide was uploaded by Cassidy Schap on Sunday September 27, 2015. The Study Guide belongs to GEO 401 at University of Texas at Austin taught by Daniel Breeker in Summer 2015. Since its upload, it has received 19 views. For similar materials see Physical Geology in Geology at University of Texas at Austin.
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Date Created: 09/27/15
they only chose the rock samples that will be very clear what it is if you know what you re looking for not multiple choice mostly short answer fill in the blank dont forget about the tectonics lab don t just focus on the rocks all questions but one will be related to samples might ask you to arrange some of the rocks by metamorphic rate rocksminerals are labelled sep wont be any confusion abt whats a rock and whats a mineral might give you several rocks tell you that all but one are either igmetsed have to pick out the one that doesn t belong COMPOSITIONAL lAYERS MECHANICAL LAYERS continental crust lithosphere 1070 km l 150200 km core ferences bt the compositional layer I layering scheme osition of each of the layers inner 939 core wont need to know depthsdensities of the layers I I l I need to know the names of the layers 2900 km 6396 km 5 50 km 660 km Converqent Boundaries Form at the intersection of two plates as they approach each other One plate usually subducts under the other the densest plate will subduct Characterized by compressive stresses Examples Eurasian PlateAfrican plate the Alps lndoAustralian plate and Eurasian plate the Himalayas Nazca Plate and South American Plate the Andes Diverqent Boundaries Form where two plates are pulling apart Characterized by tensile stresses Gap created by separation of plates is filled with new igneous rock typically basalt and gabbro from the upwelling asthenosphere Examples The MidAtlantic Ridge East Pacific Ridge East African Rift Zone Transform Boundaries Form where two plates slide past each other Characterized by shear stresses Examples The San Andreas Fault the Northern Anatolian Fault Turkey Know what each of these are and maybe an example of each be able to tell what happens at each mtns ridges upwelling etc won t be calculationsmath crap MINERALS Mineral Important Properties A Talc Soft scratches easily with a fingernail Feels smooth soapy Can be several colors including blue and pink CD 9 Gypsum Soft but does not feel as smooth as talc will feel frictioney like g fingernails on a chalkboard when scratched Usually white g Calcite Fizzes with HCI Rhombahedral looks like a squashed cube 1 Halite Cubic usually white tastes salty Relatively soft can be scratched with v a penny A Quartz Fractures conchoidally often grows as 6sided columnar crystals with pointed ends 2 Garnet Grows as rounded often 12sided crystals like a soccer ball except with g rhombuses for the faces Fractures conchoidally usually dark red to 8 brown Can39t by scratched by anything in the tray AI Olivine Green glassy Mineral samples are often sugarylooking masses of small g green crystals In igneous rocks will look like green glass Orthoclase Usually pink with 2 cleavage planes approximately 90 from each other 93 Plagioclase Milky white blocky shiny 2 cleavage planes approximately 90 from each other Hornblende Black appears splintery shiny 2 cleavage planes 120 60 Augite Dark colored black or greenishblack blocky crystals matte finish 2 v cleavage planes 90 m Hematite Streaks red Can be either red or silverygrey H a g g Magnetite Magnetic Usually black feels very dense g Galena Silver cubic feels very dense Streaks black g Biotite Black flaky very shiny 339 Muscovite Flaky very shiny Translucent greenish sheets There are like 16 of them that s a lot to have to remember 1st thing w the mineral is actually linking it with the igneous rock know the minerals in the igneous tray would benefit us to know them well there are 8 they are the most common in igneous rocks remember 2 things about each mineral something that s unique to that mineral and something that will help you differentiate it from st that looks similar 3 shiny black minerals biotite hornblende audite pyroxene all look rly similar esp in a rock biotite is usual p easy to figure out b is a mica flaky mirrorlike shiny nothing else is that dark and flaky dont worry about memorizing hardness etc hornblende look at the cleavage planes they re at an angle at 60 degrees tends to look pretty splintery surface has linear fabric to it augite v hard to ID so remember it s dark coloredblocky has 2 planes of cleavage at 90 degrees easiest just to eliminate the other 2 options and then you re left w augite w hornblende a lot of the time it breaks w a kind of stairstep pattern on surface might look like it has little stripes on it not a clean break hornblende esp in igneous rocks tends to grow in long rod shaped crystals dont try to memorize whole chart just find ways to ID so that you ll remember them and be able to ID in context focus on igneous minerals but for other ones you can usually group them p easily by their hardness if you re not sure what mineral is if you can scratch it w a penny you know you re in that top group if it s harder than a penny becomes a little more complex but color is often a good diagnostic mica is so distinctive that they re kind of in their own v distinct group gypsum feels like fingernails on a chalkboard hematite galena magnetite are only three in tray that will produce distinctive streak everything else gives a kind of greyish white whatever wont need to know the different uses for the various mineralsrocks don t rly have to memorize anything new W reaction series in mafic rocks just replace hornblende w augite remember mafic ultramafic intermediate felsic ultramafic usually green olivine study learning all the same things for rock ID and reaction series know the name of a coursefine grained rock in each category remember 2 rocksminerals that are assoc w each section 3 rocks that dont quite fit the classification kspar is pink mineral assoc w felsic rocks 2 that are way too light dont feel like rocks one light one dark quartz also assoc w metamorphic felsic clark one is scoria light one is pumice intermediate are prob hardest ones to remember conchoidal frac is representative of quartz glass neous ROCKS other one is obsidian there are no minerals in obsidian remember horn lendeplag feldspar v common in intermediate rocks actuallyjust lava that was cooled so quickly that minerals didnt have time to form basically just glass color doesnt tell you much because there are no minerals to ID CC EUltramafic Pyroxene Mafic EH rain 3ISE JITIIl Biotite 394 Oligoclase KSpar 539 M D Residual Phases Fem t gD SCOV e Last to crystallize Q Quartz C quotB Igneous rock classification Composition gt Felsic Intermediate Mafic Ultramafic 2 Texture l 2 Vesicular Pumice Scoria m FineGrained Rhyolite Andesite Basalt Porphyritic Porphyritic Andesite g CoarseGrained Granite Diorite Gabbro Peridotite C E Pegmatitic Granite 39D Pegmatite Important Facts 1 Obsidian volcanic glass No minerals because there is iffk Vv no crystal structure Same elemental compositions as felsic and intermediate rocks J quot1 Extrusive rocks are finegrained because they cool quickly 3 intrusive rocks are coarsegrained because they cool slowly quot l Porphyritic texture implies a more complex cooling history remember the vocab phenocrysts i not the same as porphyroblasts f 1 Large crystals phenocrysts WREMEMBER THESE 97 32 39 I 33933 Finegrained background groundmass understand intrusivevextrusive rocks 4 Know the most abundant minerals and characteristic colors of each compositional qroup Felsic pink or white Kspar quartz muscovite Intermediate gray plagioclase white or light grey hornblende Mafic black Plagioclase dark grey augitepyroxene Ultramafic green Olivine augitepyroxene Sedimentary Rocks The energy of the environment is NOT the same as sedimentary maturity Sedimentary maturity gt how far the sediment was transported before being deposited and lithified to form a rock Rocks that formed close to the sediment supply are immature and rocks that formed far from the sediment supply are mature This is NOT the same thing as the age of the rock The degree of roundednessanqularitv tells us how far the sediment was transported before deposition As sediment is transported sharp corners are broken off 80 more rounded more sedimentologically mature The degree of sorting also tells us how far the sediment was transported poorly sorted rocks form close to the sediment source and wellsorted rocks form far from the sediment source The mineral composition also varies with transport distance Over time feldspars and other silicate minerals break down into quartz and clays So if there are a number of different minerals the sediment is immature But if it is almost entirely composed of quartz andor clay it must have been transported for a long time gt it is mature Immature rocks Breccia arkose conglomerate Mature rocks shale siltstone quartz sandstone Energy of the environment gt how fast the water was moving when the sediment was depos ed Grain Size tells us about the energy of the environment the larger the grain size the higher the energy of the environment CLASTICS Extremely CoarseGrained gt 2 cm pebble Rounded clasts gt CONGLOMERATE Angular clasts gt BRECCIA FineGrained to Very CoarseGrained sand SANDSTONE Grains not visible Feels gritty gt SILTSTONE feels smooth gt SHALE NONCLASTICS Fizzes viqorously with HCI Finegrained dense may contain fossils gt LIMESTONE Finegrained light breaks easily gt CHALK Composed of many shell fragments gt COQUINA Does not fizz with HCI Black shiny lightweight Will mark the paper gt COAL Very smooth uniform rock conchoidal fractures gt CHERT still sed rocks just not clastic coal chert coal p easy bc usually doesnt really resemble any of the others chert is hard b just looks like dirty quartz look for conchoidal fracture sedimentary maturity and the energy of the environment are not the same thing energy of enviro is how fast they were going when they fell out of suspension maturity is how far theyve come from their source when mtn is close to water source going to get a whole mixture of grain sizes when water is way far away the sorting is going to be a lot better more distance better sorting what determines when you deposit anything youre carrying is when you no longer have the energy to keep carrying it major thing to take away is that when you re looking grain size is important sep as clastic v non clastic grain tells you what kind of environment they came from have a whole bunch of samples sort them by grain size 2 with coarse grain size can dist them based on roundness of grains once you see one w grain size same as beach sand it s sandstone tricky is differentiating bt shale and siltstone pick them up which one feels gritty and which one is smooth diff is that shale is made entirely of siltstone has little grains of stuff nice thing abt nonclastic is that a lot of them are limestone 3 will fizz w HCI major diff is texture v consolidated few tiny fossils limestone looks like made of tiny shells it s coquina Metamorphic Rocks Metamorphism changes in the texturemineral composition of a rock WITHOUT melting Although mineral composition can change the composition of the final rock is determined by the elements within the parent rock Remember that felsic minerals contain a lot of Si Al K Na and mafic minerals contain Si Fe Mg Ca Clay minerals can contain all of these elements Metamorphic grade a measure of the increase in heat and pressure that the rock was exposed to Larger grain size gt higher metamorphic grade because the crystals have a longer time to grow and develop Foliated texture gt higher metamorphic grade due to high pressure under stress planar minerals orient themselves perpendicular to the stress direction Increasing degree 01 dcl ummu on A gt i u Mints appear jurncl and ituurnhtc wmcnc increases Clux mincnls w I I39 s 39 I ippt u Amplulx I I xi inn LII app 1 dimppcar increases I I 39 I quurl ndslonc shulc II mckinnc busull granite bod n L39 k grun gneiss mch um hi gh gm d U nwtamnrphic grade We didn39t study serpentine in the minerals lab but it is a dark green fibrous mineral that forms from the alteration of peridotite in the presence of water to form serpentinite Shale is composed of clay minerals In a slate these clay minerals begin to convert to mica minerals eg muscovite biotite and as the mica minerals grow slate becomes phyllite which is much shinier thanks to the growth of these mica minerals Limestones always metamorphose to marble gt if you start with CaCOs the only rock that you can make is one that is also composed of CaCOs so that metamorphosis is only a textural change Marble can be a high or lowgrade metamorphic rock Similarly quartz sandstones can only form quartzites Grain size increases and grain boundaries fuse with increasing metamorphic grade classified by composition and by texture similar to igneous larger crystals indicate that the rock was sitting there forming crystals under high temppressure for longer met rate is basically how far away you are from starting point when asked for possible parent rock say shale met is solid state process you re not melting rock you re just rearranging the content be of high pressuretemp met grade key indicator is crystal size as grade goes up so does crystal size slate shale phyllite has ripples gneiss slate v shale the way they sound can diff them wont be asked that gneiss has color bands phyllite you may see garnets marble tends to look very sugary difficult to differentiate from a quartzite
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