Download Rock Classification Notes 2014

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EQ: How are rocks
formed?
Standard S6E5.c
Classify rocks by their
process of formation.
EQ: How Are Rocks Classified?
• What three characteristics
do scientists use to identify
rocks?
• What are the three groups
into which geologists
classify rocks?
• What is a rock’s texture?
• What do the three major
groups of rock have in
common? How are they
different?
How geologists Classify Rocks
• Rocks are made of minerals and a mixture
of other materials
• Some rocks are made of a single mineral
• When studying a rock sample, geologists
observe the rock’s texture, origin and
mineral composition
A Rock’s Texture
• A rock’s texture is the size, shape, and pattern of
the rock’s grains
Grain Size
a. fine-grained (small-basalt)
b. coarse-grained (large-granite)
Grain Shape
a. smooth and rounded (conglomerate)
b. jagged (breccia)
Grain Pattern
a. foliated (gneiss)
-lie in flat layers
-wavy, swirling patterns
b. nonfoliated (marble)
c. looks like rows of multicolored beads
d. occur randomly
No Visible Grain
a. have no apparent grains
. vy,
Mineral Composition
• By looking at a small sliver of a rock under a
microscope, geologists can observe the size and
shape of the crystals and identify the minerals
the rock contains
• Also, geologists can do tests to identify the
physical properties of the minerals inside the
rock.
•
•
mafic= dark-colored rocks (poor in silica) (basalt)
felsic = light-colored rocks (rich in silica) (granite)
Rock Origin
Origin - how and where the rock was formed
1. igneous rock = forms from the melting, cooling and hardening of
molten rock
a. extrusive= formed above the surface (lava)
b. intrusive = formed below the surface (magma)
2. sedimentary rock = forms in layers from other
rocks, plants, and animals through a
process of weathering,
erosion, deposition, compaction and cementation
a. clastic rock
b. organic rock
c. chemical rock
3. metamorphic rock = formed when existing
rock is changed by heat, pressure, or chemical reactions
a. foliated rock
b. nonfoliated rock
Compare and Contrast Rocks
Compare – Rocks in each group make up
the Earth’s crust and are composed of
minerals and other materials
Contrast – Rocks are different in the way
they are formed