rocks building blocks of the earth’s crust. earth’s layers
TRANSCRIPT
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RocksBuilding Blocks of the
Earth’s Crust
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Earth’s Layers
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Chemical Composition of the Earth
Element Symbol Percent Iron Fe 34.6% Oxygen O 29.5% Silicon Si 15.2% Magnesium Mg 12.7% Nickel Ni 2.4% Sulfur S 1.9% Calcium Ca 1.1% Aluminum AL 1.1%
Total 98.5%
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Chemical Composition of the Earth’s Crust
Element Symbol Percent Oxygen O 46.6% Silicon Si 27.7% Aluminum Al 8.1% Iron Fe 6.0% Calcium Ca 3.6% Sodium Na 2.8% Potassium K 2.6% Magnesium Mg 2.1% Total 98.5%
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Where the Rocks Are … The Crust
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What Is a Rock?A rock is a mixture of minerals!
What is a mineral?• naturally occurring (not man-made) • inorganic (not part of or a product of a (once)
living organism ) • solid (not made of liquid or gas)• chemical compound• with a definite chemical structure which
gives it unique physical properties.
Minerals are the building blocks of rocks.
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Minerals
• minerals are compounds and compounds are composed of elements
• What are the most common elements in the crust? Oxygen (O) and Silicon (Si)
• the most common minerals are silicates (contain silicon and oxygen)– the most common silicate – quartz
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Physical Properties of Minerals
• Hardness – what minerals can scratch it or be scratched by it
• Cleavage – how does it break … along planes?
• Streak – what does the powdered form look like
• Color – what colors are common
• Density – the mass of a given volume
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Cleavage
Calcite Halite
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Rocks are divided into three major groups based on the methods of formation
1. Igneous rocks … from cooling lava or magma
2. Sedimentary rocks … from compacted sediments
3. Metamorphic rocks … meta (change) morphic (form) … rocks changed by extreme forces
Rock Classification
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Rocks Classification
• Rocks are further subdivided by
–mineral composition• what minerals are present in large
quantities
– texture• what is the size of the mineral
crystals (grains )
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Igneous Rocks
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Igneous RocksFormed when molten rock cools and solidifies
Magma
Lava
geollab.jmu.edu/Fichter/ IgnRx/Intrusiv.html
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Volcano
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Explosive vs Non-explosive
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Magma vs. Lava
Magma• intrusive – below the
surface
• gathers in large bodies called plutons
• may become lava
• cools slowly – forms large crystals
Lava• extrusive - above
the surface• expelled from a
fissure or a volcano• begins as magma• cools rapidly – forms
small or no crystals
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Mineral Composition of Igneous Rocks
Rich in silicates• lots of feldspar,
quartz, and other silicates
• lighter color• more viscous –
extrusives form steep volcanoes
• continental crust
Poor in silicates• lots of iron and
magnesium rich minerals
• darker color• less viscous –
extrusives form large flows
• oceanic crust
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Types of Common Igneous Rocks
Extrusive
(Volcanic)
Intrusive
(Plutonic)
Rich in Silicates
Rhyolite Granite
Poor in Silicates
Basalt Gabbro
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Igneous Rocks
Rhyolite
Gabbro
Granite
Basalt
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Other Important Volcanics
• Pyroclastics – also called ejecta - thrown from the volcano – cool very quickly
Obsidian – volcanic glass, a unique rock containing NO MINERALS
Pumice – frothy volcanic glass
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Sedimentary Rocks
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Sedimentary Rocks
• formed from sediments (particles) that settle in great amounts and are cemented together under great pressure
• sedimentary rocks cover some 80% of the Earth's crust
• generally, the only type of rock to contain fossils
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Sedimentary Rock Formation
Clastic – particles deposited by water, wind, or ice
Chemical – particles precipitate from solution
Organic – growth in place (eg, coral reefs)
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Clastic–basic sedimentary rock.
–accumulations of pieces of broken up (eroded) rock (clasts) which have piled up and been "lithified“ (turned to rock) by compaction and cementation
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Queen’s Throne, Utah
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Clastic Sediments
• formed from the erosion of other rocks
• most sediments are carried by rivers and are deposited in great amounts in the ocean
• under great pressure, these particles are cemented together
• classified by particle size
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Clastic Particles and the Corresponding Rocks
Particle Rock
Gravel Conglomerate
Sand Sandstone
Silt Siltstone
Clay Claystone
Shale
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Chemical
–some form when water conditions change causing solids to precipitate out of solution
–some form when standing water evaporates, leaving dissolved minerals behind
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Limestone
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Chemical Sediments
Deposit Rock
Calcium Carbonate Limestone
Calcium Magnesium DolomiteCarbonate
Sodium Chloride (Salt) Halite
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Organic– accumulation of sedimentary debris
caused by organic processes– shells, bones, and teeth (calcium)– these bits of calcium can pile up on the
seafloor and accumulate into a thick enough layer to form an "organic" sedimentary rock
– Limestone can form this way; also, lignite, bituminous coal
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Metamorphic Rocks
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Metamorphic Rocks
• metamorphics get their name from "meta" (change) and "morph" (form)
• the rock is moved into an environment in which the minerals which make up the rock become unstable and out of equilibrium with the new environmental conditions
• in most cases, this involves burial which leads to a rise in temperature and pressure
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Metamorphic Rocks• the metamorphic changes in the minerals
always move in a direction designed to restore equilibrium
• any rock can become a metamorphic rock, including another metamorphic rock (can become a different metamorphic rock)
• a metamorphic rock exposed to too much heat will melt and become ???
• common metamorphic rocks include slate, schist, gneiss, and marble
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Metamorphic Rock - Gneiss
www.nearctica.com/geology/ mineral/metamor.htm
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Types of Metamorphism
Regional• areas of great
amounts of pressure (during mountain-building)
• usually associated also with high temperatures
Contact• near magma
chambers (plutons)
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Types of Metamorphism
Regional• areas of great amounts of pressure (during
mountain-building), usually associated also with high temperatures
• foliation of rocks present … pressure causes tabular minerals in the rock to grow parallel to each other and perpendicular to the direction of pressure (stress), generating a mineral alignment termed a foliation
• rocks often look folded or wavy
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Foliation
Slate
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Metamorphic Rock
www.aqd.nps.gov/grd/usgsnps/ rxmin/rock3.html
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Types of Metamorphism
Contact• near magma chambers (plutons)• rocks in “contact” or near-contact with the
magma are baked• new minerals are formed• rocks do not conduct heat well (they are good
insulators) so the zone of contact metamorphism is usually relatively narrow
• marble results from the contact metamorphism of limestone
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Metamorphic Rock
Marble
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The Rock Cycle
www.canadianrockhound.com/ junior/rock_cycle.html
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• Many are extrusive volcanic islands– Eruption eventually above the surface of the water:
Montserrat, Mt. Pelee, many others– Eruption below the surface and uplifted: St. John,
St. Thomas
• Some are flat limestone islands– Aruba, Anegada, Anguilla, Bonaire, Curacao
• St. Croix is sedimentary, but has more complex origin
• Barbados is an accretionary wedge.
Likely geological origins of Caribbean islands