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Lecture 7

EESA06H3 Lecture Notes - Lecture 7: Feldspar, Gypsum, Talc

Environmental Science
Course Code
Nick Eyles

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EESA06 Lecture 7 Page 1
EESA06 Lecture 7
Galapos Islands t in Equador, hotspots
- Hotspot trails t old dead volcanoes, flat tops (from erosion), below seas level, dead volcano
- Hotspots t majority occur on oceanic plates
- Relative Ages of islands: the youngest island above the hotspot, eventually go under sea level,
systematic aging of the rocks as you go down the trail
- Gives us a clue of plate movement
- Bathymetric t map that shows water depths
- Islands after 3 million years become completely submerged
- Phreatomagmatic t water + volcanic activity, violent releases
- Geologists like this area because there is No vegetation = young landscape, still actively evolving
- Barrel Cactus are the pioneer/first plants grow in cracks of lava,
o Prickly pear cactus another pioneer plants, eaten by giant tortoises, evolution of long
wooden stems to avoid being eaten
o Blue footed booby t bird with nostrils underneath eyes, due to evolution
- Aa lava (rocky), pohoehoe lava (ropey)
- Pyroclastic layers of ash that falls on the
land that blows out underwater, think of a
Zsnow avalanche[ZZvµv
water - laminated sediments
- Scoria t large pieces of burnt rock found
around cinder cones
- Trace fossil t track of organism, like
footprints, turtle tracks to lay eggs
Rocks and Minerals: Clues to Ancient Environments
- Lithification t to turn a sediment into rock
- Compaction t to squeeze water and air
out of something
Differences Between Rocks and Minerals
- Rock t is a naturally formed consolidated material, composed of grains of one or more minerals
- Mineral t is a naturally occurring, inorganic, crystalline solid that has a definite chemical
composition. They are the building blocks of rocks.
- Igneous rocks t to be born of fire, extrusive and intrusive
- Crystallography t the study of different shapes of crystal and diagnostic diff mineral types
Minerals 4,500 different types but
- The most important group are the silicate minerals
containing silicon and oxygen and accounts for 90% of all
minerals. Few minerals dominate ex:
o Quartz t (silica = SiO2 = silicon plus oxygen)
o Olivine (Mg, Fe SiO4) t mantle
o Feldspars (largest subgroup, shiny field crystals,
common in shield rocks, composite soil, semi-
precious stones) - crust
o Pyroxenes (ex: augite)
o Mica
o Clay minerals such as kaolinite, montmorillonite t result of weather of other minerals,
electrical properties, dictate whether soil is fertile or not

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EESA06 Lecture 7 Page 2
Silicate Structure and its effects on
magma viscosity
- According to how
tetrahedron are assembled
- Isolated silicate structure t
found in basalts
- Single Chains, Double
Chains, Sheets and
- Controls the thickness of
magma, rocks we find,
shape of volcano etc.
- Quartz is the key mineral
that thickens magma (less
in basalt)
- Basic rocks lack silica,
Acidic rocks have higher
concentration of quartz (Ex: Granite, Andesite, more than 50% is quartz)
How do we identify different minerals?
- Color t most noticeable by least accurate
- Streak t color when mineral group to a fine powder on streak plate
o Ex: hematite t red/brown
o Silicate minerals do not streak
- Hardness (scratchability)
o D}Z[Zvo-10)
Talc (very soft) = 1
Diamond = 10
Sedimentary Environments
- Locations where sediments
- Highest mountains to deepest oceans
- Different environments t produces
diff type of sedimentary rock
- Continental Shelf t shallow sea floor
- Slope t going down into deep sea
- Abyssal Plane t deep sea
Grand Canyon t Metaphoric rock layer
covered by sedimentary rock
- Tells us about Fossils, plate movement
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