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Easc 101 Mid Term Notes.docx

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Earth Sciences
EASC 101
Cindy Hansen

Easc 101 Midterm Notes Minerals 1. Rocks and minerals defined: -Rock is an aggregate of one or more minerals (calcite 1) or many (granite, limestone) -Mineral is naturally occurring not synthetic, inorganic, and solid in matter definite chemical composition. Quartz SiO2, olivine [Fe, Mg]SiO4. Ordered atomic structure that repeats itself, as they bond in an orderly fashion as the mineral grows. 2. Mineral properties identifiable characteristics: -physical and optical properties. -cleavage: how a mineral breaks. Minerals break along plane surfaces due to the alignment of bonds within the minerals surfaces of weakness. -Fracture does not break along plane surfaces, instead it is random jagged breaks (irregular), or if breaks along smooth curved surfaces (conchoidal fractures) -some minerals break with cleavage in some directions and fracture in other -Hardness is the ease in which a mineral can be scratched -Mohs Hardness scale is used with 10 points 1 2 3 4 5 6 7 8 9 10 talc gypsu calcit fluorite apatit feldspa quartz topaz corundu diamon m e e r m d -Tall gills can force apart oreos quicker than clumsy dudes -Lustre how a mineral reflects light (metallic is shiny, non can be light or dark) -Crystal form is the shape a mineral will grow in an unrestricted space which is uncommon, look for fracture surfaces, largest crystals are gypsum in Mexico -react to HCl is a property as it eats away -streak is the colour of the powdered form of the mineral (good for metallic) -colour can be used though not best and variable due to many chemical properties -magnetism and optical properties as well -diagnostic properties are those that are most useful in identifying a particular mineral 3. Seven major mineral classes: -Silicates contain Si and O in a combination and make up 95% of earth’s crust, feldspars and quartz, most abundant on earth, building block is silica tetrahedron with net charge of -4 thus it needs to bond with cations or share with oxygen for electrons, further divided into nonferromagnesian and ferromagnesian silicates (with Fe and Mg and not) -Native pure elements is a group -Oxides have oxygen -Sulfides with sulfur -Sulfates with SO4 -Halides with Cl, F, Br or I -Carbonates with CO3 such as calcite and dolomite 4. Mineral groups varieties and species -mineral groups: minerals that are similar chemically and have the same crystalline structure. Ex all feldspars have Si3O8 and can be divided further by k-spar and plag. K is K, plag is Na, C or a combo of the two can be present -Olivine group is ferromag silicates, commonly found as small grains with rocks under the microscope -Pyroxene is ferromag silicate, black or dark green broken grains show 2 cleavages at 90, fools gold and augite -Amphibole group is ferromag silicate, black or dark green broken grains 2 cleavages but not at 90, hornsblend -Mica group breaks into sheets 1 cleavage, mica biotite is ferromag silicate, no colour is mica that is muscovite which is nonferro -Feldspar is most common in earth with 2 species with K and plagiocite with many colours and 2 cleavage at 90 -Quartz is SiO2 and nonferro that is hard and second most common in earth’s crust, 7 on Moh’s scale, many colours+conchoidal fractures -Calcites CaCO3 carbonates from calcite ppt from the sedimentary rock limestone, 3 cleavages not at 90 and HCl reaction Plate Tectonics -continental drift hypothesis 1915 by Wegner that 200 million years ago all were together in Pangaea and since then drifted apart -Evidence includes fit of continents together such as Africa and south America and climates, matching eroded mountains ranges of NA and Euro, fossils of same animals in SA and Africa, glacial deposits are found in southern continents and in other places, paleoclimate belts align for similar characteristics -How PT theory came: step 1 seafloor spreading hypothesis by Hess mapped pacific ocean seafloor revealing ridges (MORs) were locations where new ocean crust as being formed from sea ocean spreading and that old ocean crust sunk back into the earth at the deep ocean trenches (subduction), Hess thought mantle convection process is movement of ductile mantle rock -Step 2 is evidence: Matthews and Vine present paleomagnetic data from seafloor as evidence of spreading, as lava cools iron aligns itself with the existing polarity causing magma intruding fractures at MORs and then followed by cooling which traps the magma field, magnetic field sometimes reverses in earth’s history, a ship is used to record with magnetmeter, positive anomalies is when crust is same as earth’s field, negative opposite, parallel stripes of alternating reversed polarities on either side of the ridge makes mirror images providing that spreading occurs at the ridge crest -Step 3 Hot Spots: Wilson explains presence of active volcanism formed at deep mantle hot spots that the plates travel over, volcanism pushes up through the overriding plates producing a chain of volcanoes that will increase with age in distance from active hot spot -Step 4 transform faults: Wilson predicts the presence of TFs connection to offset MORs, confirmed using data off west coast with paleomagnetic -Theory comes together as earth surface broken into plates, diverge at mid atlantic ridge and converge at ocean trenches, and slide past each other at transform faults, and pass over deep mantle hot spots, plates move from mantle convection 3. Further evidence for Plate Tectonics: the ocean floor has been fully mapped revealing a continuous midocean ridge system (MOR chain), trenches, location of various hotspots deep sea drilling project. numerous countries participate -> drill into sea floor and take rock as continuous core reveals that oceanic crust is youngest near the crest of MORs, oldest furthest away. sediments above the oceanic crust are thinnest nearest to the ridge crest and thickest furthest away. satellites can measure the distance of spreading (cm/year). VERY SLOW where the colours are red the crust is the youngest, oldest is shown as blue. ridge systems are high elevation peaks on floor. -Lithosphere breaks
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