Download ROCKS and how to identify them

ROCKS
ROCKS
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Rocks: naturally occurring
combinations of minerals,
fossils or other hard
materials.
• classified by the way in
which they form.
• 3 rock types: igneous,
sedimentary and
metamorphic
IGNEOUS ROCKS
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vent
lava
Igneous Rocks: former magma
(molten rock), which cooled and
crystallized into solid rock
Intrusive (Inside) Igneous
Rocks: form as magma cools
slowly beneath Earth’s surface
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lan d surfac
e
conduit
Slow cooling rate allows crystals to
grow large, so they are very visible
magma
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Extrusive Igneous Rocks: form
as lava (former magma) cools
quickly at Earth’s surface
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Anatomy of a Volcano
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Rapid cooling produces small
crystals, not readily seen by the
unaided eye.
Volcanic in origin
Cooling may be so rapid that glass
is produced (Obsidian)
Intrusive Igneous Rocks
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Granite: a coarse rock formed
from the cooling of magma within
the Earth (intrusive)
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Composed of various amounts of
quartz, feldspar, muscovite, biotite,
and hornblende.
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Continental crust (that stuff we live
on) is primarily composed of
granite…know that.
quartz
biotite
mica
(*)
feldspar
Extrusive Igneous Rocks
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Basalt: dark, fine-grained
igneous rock
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Fine grained because it
formed quickly or slowly?
occurs as lava, sometimes
accumulating to thicknesses
of 1000s of feet and covering
1000s of miles cools rapidly.
Volcanoes which produce
basaltic lavas are nonexplosive
Oceanic crust is composed
of basalt…know this!
Igneous Rock Video
Basalt – Extrusive Igneous Rock
Vesicular
Volcanic Bomb (*)
Gases released near the
surface of a lava flow create
bubbles or vesicles, which
are “frozen” in stone.
Amygdaloidal
(*)
Basalt – Extrusive Igneous Rock
Pahoehoe: feature which
forms on the surface of a
very fluid basalt flow.
Much like the skin on a
bowl of tomato soup –
the surface in contact
with the air begins to
crystallize, while the fluid
lava below continues to
flow. This drags the
upper, still plastic,
surface into a series of
smooth wrinkles.
Basalt – Extrusive Igneous Rock
The Bottom side of this
pahoehoe is rough and
jagged and is called
Aa.
Basalt – Extrusive Igneous Rock
Flow banding
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Obsidian: volcanic glass
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glassy, lustrous and
appearance makes it easy to
distinguish from all other rocks
cooled so quickly that the
minerals could not crystallize.
Colors vary from black to red,
black & red (mahogany), gray,
green, iridescent, snowflake.
Apache Tears are little nodules
of obsidian
Apache tear
Snowflake
SEDIMENTARY ROCKS
Sedimentary Rocks:
layered or stratified rocks
• Sedimentary rocks form from
compaction or cementation
• Compaction: a squeezing
together of
particles/sediments
• Cementation:
particles/sediments get glued
together by dissolved
minerals
• 2 types: Clastic Sedimentary
Rock and Chemical
Sedimentary Rock
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Sedimentary Rocks
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Clastic Sedimentary Rocks:
composed of particles of preexisting rocks
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fragments show evidence of
transport
Examples: Shale, Sandstone
Chemical Sedimentary
Rocks: composed of solids
which precipitated from
solutions (like salt from
evaporated water) or organic
process (like compacted shells
from marine organisms)
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Examples: Limestone, rock salt,
coal Sedimentary Video
Sandstone
Shale
Sandstone and Shale – Sedimentary Rock
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Sandstone: composed of
cemented sand grains
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identified by its sandy
texture and gritty feel
form in beaches, sand
bars, deltas and dunes
Shale: very common rock
made of silt and clay
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Very thin with splits along the
planes.
gray to black, or brown to dark
red
forms in lakes, swamps, and
deltas
Coconino Sandstone,
the result of a Permian
age coastal dune field
Black shale, from the Middle Cambrian
sea.
COAL – Sedimentary Rock
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Coal: decomposed remains of
vegetation which accumulated in a
wet, low oxygen environment, such
as a swamp or marsh
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Coal (sub-bituminous) out of the
Cretaceous Dakota Formation of
north-eastern Arizona.
Examples include: Peat and Lignite
used as fuels
Sedimentary Rock
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Features of sedimentary
rock include:
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Layering
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ripple marks
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mud cracks
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salt casts
Sedimentary Rock
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Features of sedimentary
rocks are clues to how
the rocks are formed,
and help us understand
the history of the Earth
Weathering, Erosion, and Deposition
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Weathering: breaking down of
rock through contact with the
Earth's atmosphere and waters
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Erosion: process by which soil
and rock are removed from the
Earth's surface by wind or water,
and then transported and
deposited in other locations
Deposition: process by which
sediments, soil, and rocks are
added or deposited to an area
Funny Video
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All rocks on Earth are locked into a
system of cycling and re-cycling
known as the ROCK CYCLE.