Transcript Geology Part II: Rocks

Geology Part II
• The Rock Cycle
• Rocks:
– Igneous
– Sedimentary
– Metamorphic
• Geologic Profiles
• Geologic Time
– Relative
– Absolute
– Radioactive Dating
Rocks are minerals?
• an indefinite mixture of
naturally occurring
substances, mainly
minerals.
•
various combinations of
minerals and organic
substances
•
• range in size from tiny http://en.wikipedia.org/wiki/Sedimentary_rock
pebbles to mountains.
•
• make up the earth’s crust.
Rocks are not always solid
• As discussed in plate
tectonics magma is
liquid rock
• While the composition
of this basalt flow have
the same composition,
• the smooth pahoehoe
lava was hotter than
the jagged aa lava.
• Soil and clay are other
examples of nonsolid
rock
Igneous Rocks
• Fire Formed
• Hardens as magma
cools
• “original rock”
• Lava is on the Earth
2 types of Igneous Rocks
1. Intrusive cools inside the
Earth
Slow cooling= big crystals
• Ex.granite
2. Extrusive cools outside
the Earth
Fast cooling = tiny crystals
• Ex. obsidian
Types of Intrusive rocks
• Granite is the most
common and is referred
to as “mountain guts”
• Diorite – iron and
magnesium
• Gabbro – dark, large
crystals
• Peridotite – green, most
of upper crust
Yosemite Rock formation
http://www.nps.gov/yose/planyourvisit/formations.htm
• “El Capitan is the largest
monolith of granite in the
world.”
• Formed deep
underground and then
uplifted by plate tectonics
and shaped by erosion
• Age can be determines
by radioactive dating
Extrusive Igneous Rocks
• Basalt – common, hard,
dark
• Andesite – began cooling
in crust finished on
surface large/small
crystals
• Rhyolite – cooled slowly
then fast
• Pumice – light, spongy
look
• Obsidian – volcanic
glass, cools fast
Metamorphic Rock
• Created by 1 of 2
processes
• Regional process – most
common, heat and
pressure over large area
• Contact – heat and
pressure next to magma
chambers
• 2 types: Foliated,
Nonfoliated
• Formed from preexisting
rock that has been
exposed to high heat
and/or pressure
• Enough to deform but not
melt
• Cannot determine age by
relative or absolute
(radioactive dating)
Foliated
• “layered” rocks
• Slate – made from
shale
• Gneiss – made from
granite
Nonfoliated
• No ‘layers’
• Marble – made from
limestone
• Quartzite – made
from quartz
Sedimentary Rock
• Formed at the bottom of
lakes and oceans by the
deposition of sediment
(small dust, sand, organic
material) that was eroded
by wind, water, ice from a
preexisting rock.
• Only 5% of Earth’s crust
• Time and pressure
cement particles to form a
new rock
Sedimentary rock characteristics
Breccia: clastic
•
•
•
•
Often have layers
Often contain fossils
Not very strong
Can determine
relative age by
location
– Top layers are younger
• Absolute age cannot
be determined
3 types: Clastic, Chemical, Organic
• Clastic: Most common
• Made of other rocks
• Particles accumulate and
harden in 2 ways
– Weight of upper layers
squeeze out liquids
– Minerals dissolved in
ground water act as
cement
• Weathering is an active
process
• Sandstone
–
sandsized
quartz,
variety of
colors
• Shale –
most
common,
mud, clay,
silts
Chemical
• Limestone – 50%
calcite from seashells
• Coquina – large
pieces of shell
• Chalk – microscopic
pieces of shell
• Halite – hard,
created by
evaporation
• Gypsum – soft,
created by
evaporation
• Chert – hard,
created by heat
Organic
• Coal – black, coarse,
decayed plant life
Special Features of Sedimentary
Rocks
• Layering (bedding)
• Fossils
• Geode (minerals in a
hole or cavity)
• Concretions (minerals
form around a grain
or fossil)
Rock Cycle Interactive Review
• http://www.learner.org/interactives/rockcycl
e/diagram.html
Picture Credits
• "Copyright 2009 by Andrew Alden,
geology.about.com, reproduced under
educational fair use.“
• http://www.learner.org/interactives/rockcycl
e/diagram.html
• DeJuana Aldrich