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Western University
Earth Sciences
Earth Sciences 1081A/B
Kim Luton

LAB EXAM REVIEW  Mineral  How  Cleavage/ Colour Streak Other Properties Looks like: Name hard? Fracture Talc 1 Basal (hard to  Highly variable,  White Slippery feel see cause of  commonly  small crystal  colourless/slight  size) tint of colour Calcite 3 Rhombohedral Highly variable,  White Reacts with acid colourless in pure  form but more  often has a slight  tint of colour due  to impurities Gypsum 1.5­2 Basal Highly variable,  White Chalky feel  colourless or  when powdered (chalk) slight tint of pale  color Halite 2­2.5 Cubic Highly variable,  White Salty taste usually colourless Fluorite 4 Octahedral Highly variable,  White Fluoresces in  usually  UV light colourless, purp  or GREEN  Hematite 5­6.5 Fracture Highly variable,   Reddish   N/A usually reddish   brown brown or silvery  ­shinier than  grey magnetite Foliation!!! Galena 2.5 Cubic Silvery to steel  Black High specific  grey gravity (very  heavy) Quartz 7 Conchoidal  Highly variable,  White N/A fracture usually colourless Garnet 7­7.5 Fracture Highly variable, White Resinous lustre  Usually reddish  ­resin or amber (sandpaper or brown Magnetite 5 Fracture Grey to black Grey  Magnetic  to  (coins?) black Augite  5­5.5 Prismatic Variable,  White  N/A Pyroxene generally dark  to  2 directions  green to black greenis close to 90 h Hornblende 5­6 Prismatic Variable, usually  (Amphibole  dark green to  group) 2 directions, black 60 and 120 Plagioclase  6 Prismatic Variable,  White N/A feldspar commonly white  2 directions, 90 to grey Orthoclase  6­6.5 Prismatic Variable,  White N/A feldspar commonly pink 2 directions, 90 Muscovite  2­2.5 Basal Colourless to tan  White Glittery  Mica brown appearance in  powdered form (cosmetic  glitter) Graphite 1­2 Basal (too fine  Silvery grey to  Black Slippery feel  scale to  black when powdered (pencils) observe in hand  sample) orthoclase (potassium feldspar) creamy pink color MOH’S SCALE OF HARDNESS: plagioclase (sodium/calcium feldspar) tends to be 1  Pencil Lead (1­2)    6 white or grey 2 Fingernail (2.5)    7 Porcelain Streak Plate (7) 3 Copper penny (3)    8 specific gravity: minerals with metallic lustre: 4      9 heavier than non metallic lusters TYPES OF CLEAVAGE: breaks in one dominant direction named after the “ideal” polyhedron (multi- sided, 3 dimensional shape) produced when all cleavage directions are represented in a broken specimen two cleavage directions will produce prism-like pieces of variable length (hence prismatic cleavage). Four intersecting cleavage directions will Three cleavage directions intersecting 0 ideally produce an 8-sided polyhedron (thus at 90 (right angles) produces a cube octahedral cleavage)- whoa, this is as (thus cubic cleavage), whereas three complex as we’ll go for now! cleavage directions not intersecting at 0 90 produce what looks like a leaning box - a rhombohedron (thus rhombohedral cleavage). Afew minerals do not exhibit cleavage when broken, but rather fracture in a non-planar (but still distinctive) way. Conchoidal fracture, characterized by curved, scoop-like surfaces (such as you will have probably seen in broken pieces of thick glass) is perhaps best-observed in the mineral (and, rest assured, is the only type of fracture you will be required to know for this lab. ROCKS Igneous rocks formed by crystallization of magma Sedimentary rocks composed of sediment-materials deposited at or near Earth’s surface by the settling out of air or water Metamorphic Rocks rocks (whether igneous, sedimentary, or metamorphic) that experienced a change in form or properties due to significant changes in the temperature- pressure conditions experienced by the rock and the chemical influence of fluids like water on their minerals IGNEOUS Texture phaneritic: interlocking crystals are large enough to see without magnification help aphanatic texture: constituent crystals are too small to be easily observed without magnification help Compositions: mafic (silicates—FeMg) dark coloured phaneritic: black, brown or very dark green mineral crystals aphanitic: overall dark colour felsic (feldspar/silica) light coloured phaneritic: dominance of light coloured (white or pink) minerals aphanitic: overall light colour—white, grey or pink intermediate composition equal amounts of dark and light phaneritic: equal proportion of dark and light minerals aphanitic: medium shade of colour—medium grey Names: Clastic/Detrital Sedimentary Rocks • composed of fragments/particles derived from pre-existing rocks mineral composition: • quartz=main mineral component, resistant to weathering • clay minterals, important weathering product texture: defined by grain/particle size VVV Chemical and Biochemical Sedimentary Rocks • formed by the precipitation of mineral materials from a solution • some are deposited when the concentration of dissolved ions in seawater becomes too great to remain dissolved • limestone is precipitated • fossils formed Metamorphic Rocks contact metamorphism simple “cooking” of rock surrounding a body of magma • occurs under relatively uniform pressures, platy and elongate minerals retain a random orientation regional metamorphism combined influence of increasing heat and directed pressure as lithospheric plates converge • metamorphic rocks that have formed via regional metamorphism can have foliation – a uniquely metamorphic texture that indicates the extent or “grade” of heating and pressing experienced by the rock. • The combined effect of increasing temperature and directed pressure is that platy and/or elongate mineral crystals line up in a direction perpendicular to that of the applied pressure low metamorphic grade: parent rock = shale, changes minerals to mica, producing slate medium metamorphic grade: micas become large enough to sparkle under light in a rock called schist high metamorphic grade: light and dark minerals separate into distinct bands, forming gneiss Not all rocks develop foliation (limestone and quartz which morph marble and quartzite don’t) • regardless of whether marble or quartzite are formed by contact metamorphism or regional metamorphism of their respective parent rocks (protoliths), these rock types will not develop foliation. marble=calcite, quartz=quartzite RIVER FEATURESAND FLOOD HAZARDS Streams with meandering channels (ex. thames) migrate back and forth across a flat area called a floodplain cut bank the downstream flow of a stream is faster on the outside bank (removes sediment) causing erosion—material higher up slides down into channel • steeper slope than point bar point bar builds out laterally as more and more depositions of river sediment on the inner bank is added from the slower moving current floodplain broad, flat area bordering the channel area over which water spreads when it breaches the stream’s banks during a flood We can see meander belt stages from meander scars and differences in elevation • oldest=highest elevation, youngest=lower • reflect lateral migration of meanders and downcutting of the channel to progressively lower elevations Hydrograph: graph showing water level over time compared to normal levels. shows main floods surge over short periods of time indicators of erosion: lack of vegetation on outer banks Frequency of flood of given flood level: # years in the time interval of interest (given) # flood events of a given “flood level” ex. 150 years, 30 severe floods 150/30 =5 years/1 flood or 1 flood per 5 years *river tracing activity Sediment tends to be deposited soon after the peak of a flood, once flow energy weakens it loses competence (can no longer carry the sediments as easily) gravel deposited in the main stream where water is moving fastest overflow of water from the channel onto the floodplain leads to the deposition of progressively finer grained sediment size as we get further away from the channel (sand=closer to channel, silt and clay are further back) natural levees develop closest to the channel banks -consist of sand -form from decrease in flow strength of floodwaters -can buildup from repeated flooding -serve as natural flood barriers for small floods -the silt and clay further back can form swamps cause the levees prevent floodwater to drain back into the channel Clastic Sediment Type Rock Name gravel ▯ conglomerate sand ▯ sandstone clay ▯ shale recurrence interval: average # of years between floods of a certain size hydrographs: show changes in water level over time EARTHQUAKES seismometers: detect and locate most earthquakes larger than 4.0M and many smaller ones Earthquakes occur along plate boundaries, propagated through earth as vibrations, measured and translated into seismograms by seismometers different types of vibrations travel at different speeds p-waves travel by compression • fastest o arrive first s waves travel by shear • slower o arrive after p waves difference in arrival time and knowledge of speed to determine how far away an earthquake has occurred noticeable deviation from  baseline=first P­wave S­waves: more dramatic than p  waves, marked by strong  increase in amplitude  Calculate the epicentral distance (distance between PKRO and location of the earthquake epicenter) • difference in arrival times of first P and first S waves is proportional to distance between seismic recording stations (like PKRO) and earthquake epicentre • time difference for PKRO is s wave arrival time minus p wave arrival time o (06:28:44-06:28:34=0:00:10) ten seconds or just look at graph lol. • translate S-P interval time into units of distance using the time-travel distance graph below. draw a line from the 10 second (or whatever the time difference is for your station) down to the horizontal axis, it will equate the time lag between the P and S wave arrival time to kilometers (in this case, 98 km from the pkro seismograph station. • this could be 98 km in any direction relative to this single station, Station P-wave arrival S-wave arrival Difference in Distance of time time arrival times (p- recording s) station from quake epicentre WLVO 6:28:40 6:28:54 14s 135km ACTO TYNO draw circles representing the epicentral distances for stations using the steps above (radius of the circle) from the station points on the map that will be given to us (use map’s scale). POI of circles=earthquake’s exact epicenter this method of location=triangulation. VOLCANOES lava flows: short and thick=high silica content • produces dark coloured, aphaitic volcanic rock basalt • and lighter coloured aphanitic volcanic rock rhyolite easy flowing=low silica contents mafic lava-lower viscosity, easier flow, flows long distances, low S2O high Mg/Fe felsic lava-high viscosity, slow flow, gases evaporating in magma cause eruption, light in color lava dome mound shaped protrusion develops at the summit of a volcano from slow extrusion of viscous lava. • serves as a cap with high viscosity that prevents gas from escaping. • buildup of gas/pressure under or within the lava dome can eventually lead to highly explosive eruptions Pumice forms as ‘rock froth’ that is formed when water, gas and lava mix • typically lightly coloured, lightweight, full of holes • can float on water • pulverized into tephra particles during an explosive eruption, carried great distances • higher the cloud and stronger the wind, the further away it goes • small ones go further duhhh pyroclastic flows • hot mixtures of ash, gas and rock fragments that flow down the flanks of a volcanic cone • generated at or near a volcano summit • flow downhill and away • high velocity, very dangerous • tuff rock composed of ash (dust sized tephra) and angular shards of broken rock that are all welded together • block and ash flow a type of pyroclastic flow deposit of tephra and lava (burning cloudes—nuee ardentes) crazy hot fast moving and dangerous pyro flows –funnel into valleys mud flows • loose volcanic material mixes with large volumes of water • happens when an eruption coincides with a time of increased rainfall • also happens when heat of an eruption causes a ton of snow at the summit to erupt • addition of large amounts of water to tephra at summit of a volcano produces a fluid mud slurry that flows picking up debris along the way Determining when eruptions Occurred determine the age of volcanic eruptions by dating pieces of charred wood and peat using radioactive carbon • under the deposit=older than eruption • inside deposit=burned by eruption • landslides carry pieces of wood downhill and can mix up sequence Stratigraphic sequences chronologicalize age dates for material from volcanic areas C ages=years before present. for these calculations, we will ignore the error factor (+/- #) to find out how often a volcano over the course of its history, add all these VV and then divide the total by the # of applicable eruptions (in this case, 8) ore type of rock that contains minerals with important elements including metals that can be extracted from the rock at a profit. The ores are extracted through mining; these are then refined (often via smelting) to extract the valuable element(s). locating an ore body that can be mined: majority of ore bodies are ‘massive sulphides’— bodies of metal and sulphur associated with ancient submarine volcanoes most mines have ores that combine metals of interest with other elements. massive sulphides: metals are bound to sulphur. bonding and composition of the mineral using chemical formulas. ne
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