rocks building blocks of the earth’s crust. earth’s layers
TRANSCRIPT
RocksBuilding Blocks of the
Earth’s Crust
Earth’s Layers
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%
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%
Where the Rocks Are … The Crust
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.
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
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
Cleavage
Calcite Halite
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
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 )
Igneous Rocks
Igneous RocksFormed when molten rock cools and solidifies
Magma
Lava
geollab.jmu.edu/Fichter/ IgnRx/Intrusiv.html
Volcano
Explosive vs Non-explosive
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
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
Types of Common Igneous Rocks
Extrusive
(Volcanic)
Intrusive
(Plutonic)
Rich in Silicates
Rhyolite Granite
Poor in Silicates
Basalt Gabbro
Igneous Rocks
Rhyolite
Gabbro
Granite
Basalt
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
Sedimentary Rocks
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
Sedimentary Rock Formation
Clastic – particles deposited by water, wind, or ice
Chemical – particles precipitate from solution
Organic – growth in place (eg, coral reefs)
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
Queen’s Throne, Utah
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
Clastic Particles and the Corresponding Rocks
Particle Rock
Gravel Conglomerate
Sand Sandstone
Silt Siltstone
Clay Claystone
Shale
Chemical
–some form when water conditions change causing solids to precipitate out of solution
–some form when standing water evaporates, leaving dissolved minerals behind
Limestone
Chemical Sediments
Deposit Rock
Calcium Carbonate Limestone
Calcium Magnesium DolomiteCarbonate
Sodium Chloride (Salt) Halite
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
Metamorphic Rocks
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
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
Metamorphic Rock - Gneiss
www.nearctica.com/geology/ mineral/metamor.htm
Types of Metamorphism
Regional• areas of great
amounts of pressure (during mountain-building)
• usually associated also with high temperatures
Contact• near magma
chambers (plutons)
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
Foliation
Slate
Metamorphic Rock
www.aqd.nps.gov/grd/usgsnps/ rxmin/rock3.html
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
Metamorphic Rock
Marble
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