Transcript How Do Geologists Classify Rocks?

Inside Earth Chapter 5 Notes: Rocks
http://www.indiana.edu/~g103/G103/
wk3/wk3.html
site on rocks with crystallization
demo (need 3-D glasses for one
section)
http://www.youtube.com/watch?v=fC
GrXtdSv2c
Section 1: How Do Geologists
Classify Rocks?
• When studying a rock
sample, geologists observe
the rock’s color and
texture and determine its
mineral composition
What Is Texture?
• Texture – the look and feel
of the rock’s surface
• Most rocks are made up of
grains – particles of
minerals or other rocks
• A rock’s grain gives it its
texture
How Do Geologists Describe a
Rock’s Texture?
• Terms:
–Grain size
–Grain shape
–Grain pattern
How Does Grain Size Help
Identify a Rock?
• If the grains in a rock
are large and easy to
see they are said to
be coarse-grained
• If the grains are
small they are said to
be fine-grained
How Does Grain Shape Help
Identify a Rock?
• Different rocks have
different grain
shapes – some are
smooth while others
are jagged
How Does Grain Pattern Help
Identify a Rock?
• The grains in a rock
form patterns;
Some are flat others
are wavy
What Does It Mean to Have No
Visible Grain?
• Some rocks cool
so quickly they
have no crystal
grains - glassy
• Ex. Flint
What Do Geologists Do When Texture
Does Not Give Them Enough
Information About a Rock?
• They look at the mineral’s
composition under a microscope
–A small sliver of rock allows
them to see the shape and size of
the crystals
• They use mineral tests too Scratch test, acid test, or a magnet
What Are the Major Groups of Rocks?
• Igneous
• Sedimentary
• Metamorphic
How Are Igneous Rocks Formed?
• Igneous – forms
from the cooling
of molten rock –
either magma
below the
surface or lava
at the surface
How Are Sedimentary Rocks
Formed?
• Sedimentary –
forms when
particles of other
rocks or the
remains of plants
and animals are
pressed and
cemented together
How Are Metamorphic Rocks
Formed?
• Metamorphic – formed
when an existing rock
is changed by heat,
pressure, or chemical
reactions
• Most of these rocks are
formed underground
Section 2: Igneous Rocks
What Characteristics Are Used
to Classify Igneous Rock?
• Origin
• Texture
• Mineral
composition
Where Do Igneous Rocks Come
From?
• Origin – where they are
formed
–Extrusive – rock that has
erupted on to earth’s
surface ex. Basalt
–Intrusive – rock that
formed when magma
hardened beneath earth’s
surface ex. Granite
What Is the Texture of Igneous
Rock Like?
• Texture depends on the size and
shape of the mineral crystals –
can have large or small crystals
• Porphyritic Texture – a rock
with large crystals scattered on a
background of much smaller
crystals
What is the Mineral Composition of
an Igneous Rock?
• Igneous Rocks differ in mineral
composition depending on how
much silica and other minerals
are present in magma and lava
• Higher silica forms lightcolored rocks like granite
• Lower silica forms dark-colored
rocks like basalt
How are Igneous Rocks Used?
• Tools – obsidian was used
to make ancient tools
• Building – Granite
structures
• Basalt is used to make
gravel in construction
• Pumice is used for
cleaning and polishing
Section 3:Sedimentary Rocks
What Makes up Sedimentary Rock?
• Sediment – small, solid
pieces of material that
come from rocks or living
things
What Turns These
Sediments Into Solid Rock?
• Erosion
• Deposition
• Compaction
• Cementation
What Is Erosion?
• Destructive forces break
up and wear away the
rock on the earth’s
surface
• Occurs when running
water or wind loosen
and carry away
fragments of rock
What Is Deposition?
• The process by which sediment
settles out of the water or wind
carrying it
• Sediment can include shells,
bones, and leaves. Over time the
remains of living things may
harden and change into fossils
What Is Compaction and
Cementation?
• Compaction – the process
that presses sediments
together
• Cementation – the process
by which dissolved
materials crystallize and
glue particles of sediment
together
What Are the Types of
Sedimentary Rocks?
• Clastic rocks
• Organic rocks
• Chemical rocks
What Is a Clastic Rock?
• A sedimentary
rock that forms
when rock
fragments are
squeezed
together
• Ex. Shale,
sandstone, and
conglomerate
What Are Organic Rocks?
• Rocks that are formed
where the remains of
plants and animals are
deposited in thick
layers
• Ex. Coal, and
limestone (chalk)
What Are Chemical Rocks?
• Rocks that form
when minerals
that are dissolved
in a solution
crystallize
• Ex. Rock salt is a
chemical rock
made up of the
mineral halite
Chapel of Saint Kinga
the largest among underground chapels
in the Wieliczka (Krakow, Poland) Salt mine, is actually a sizable
subterranean church carved in rock salt and
embellished with salty sculptures and bas-reliefs.
How Is Sedimentary Rock Used?
• Building materials –
sandstone (White House)
and limestone
Section 4: Rocks from Reefs
What is a Coral Reef?
• A structure of
calcite skeletons
built up by coral
animals in warm,
shallow ocean
water
How Does a Coral Reef Form?
• Coral animals absorb
calcium from the ocean
water. The calcium is
then changed into calcite
and forms their shells.
• When an animal dies,
their skeleton remains
and more corals build on
top of them
What Are the Types of Coral
Reefs?
• Fringing reefs –
close to shore
• Barrier reefs –
farther out from
land
• Atolls – ringshaped coral
island
How Can Limestone Be Found
Above the Ocean Floor?
• Limestone that begun
as coral can be found
on continents in places
where uplift has
raised ancient sea
floors above sea level
Ex. El Capitan, Texas
Section 5: Metamorphic Rocks How Do
Metamorphic Rocks Form?
• Heat and pressure deep beneath
earth’s surface can change any
rock into metamorphic rock
• Granite to Gneiss
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How Do You Classify Metamorphic
Rocks?
• The arrangement of the
grains that make up the rocks
– metamorphic rocks can be
Shale
(sedimentary)
foliated or nonfoliated
• Foliated – metamorphic rocks
whose grains are arranged in
Slate
parallel layers or bands ex. (metamorphic)
Slate
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How Is Metamorphic Rock
Used?
• Most useful
metamorphic
rocks: marble and
slate
• Uses: buildings
and statues
Section 6: The Rock Cycle
What Is the Rock Cycle?
• A series of
processes on
Earth’s surface and
inside the planet
slowly change rocks
from one kind to
another
What Drives the Rock Cycle?
• Convection
currents within
the mantle cause
the plates to
move pushing
rock back into the
mantle
What is the role of plate
tectonics in the rock cycle?
• Plate movements start the
rock cycle by help to form
magma (the source of
igneous rocks) and cause
faulting, folding, and other
motions of the crust that
help to form sedimentary
and metamorphic rocks.