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3.2 Classifying Rocks
Cht. 3 Rocks
Geologists use Characteristics to identify rocks
1. Mineral Composition : What minerals are in the rock?
-about 20 minerals make up Earth's crust
-called Rock Forming Minerals
-geologists use mineral tests to find out what
minerals are in the rocks (color, luster, streak, etc)
2. Texture: the look and feel of the rock's surface
-grains give rock their texture:
a. grain size: fine (small), coarse (large)
b. grain shape: rounded or jagged
c. grain pattern: banded (lines and layers), nonbanded (no lines or layers)
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3. How Rocks Form
a. Igneous: cooling of magma or lava
b. Sedimentary: remains of living things are pressed
and cemented together
c. Metamorphic: rock that has been changed by heat,
pressure and chemical reactions; forms deep
underground
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3.3 Igneous Rocks
"fire"
1. origin- where it came from
Extrusive: hardened lava that erupted on
Earth's surface
ex) basalt-common ocean floor
Intrusive: formed when magma hardens
inside earth
ex) granite; forms mountain ranges
2. texture: depends on size and shape of
mineral crystals
a. intrusive rocks have larger crystals
than extrusive rocks
b. rapid cooling makes smaller crystals;
slow cooling makes larger crystals
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c. Intrusive: see large chunks of minerals
d. Extrusive: fine grained and glassy
3. Mineral Composition
a. most of earth's minerals contain "silica"
b. magma/lava is low in silica- dark color
c. magma/lava is high in silica- light color
4. Uses of Igneous
a. granite- countertops, buildings, statues
b. basalt - gravel
c. pumice- cleaning and polishing
d. obsidian- sharp tools, soil
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3.4 Sedimentary
sediment
-small solid pieces of material that come
from rocks or living things
-may include shells, leaves, bones
1. erosion- water, wind, ice carry away soil
and rocks
2. deposition-particles fall out/down and
land somewhere
3. compaction- layers press down on layers
beneath them
4. cementation- dissolved minerals
crystallize (harden) and fill in cracks, gluing
layer together
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Types of Sedimentary Rock
1. clastic- rock fragments are squeezed
together
ex) sandstone, shale
2. organic- remains of plants and animals
ex) coal, limestone (fossils)
3. chemical rocks- minerals that are dissolved
in a solution crystallizes
ex) minerals deposits
4. Uses of Sedim.
-building materials and tools (flintarrowheads, cement, limestone)
- easier to cut than igneous
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Coral Reefs
How Coral Reefs Form
1. skeletons are made of calcite
2. when die-skeleton remains
3. other corals build on skeleton
• form in warm, shallow, waters
• form over thousands of years
• limestone deposits NOW are from ancient
coral reefs
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3.5 Metamorphic
"change form"
1. heat and pressure deep in earth change
any rock INTO metamorphic rock.
a. texture, crystal structure, appearance
and mineral content CHANGEs
2. Types of Metam.
*classified according to arrangement of
grains/crystals
a. Foliated- parallel layers or bands
ex) gneiss, slate
b. Nonfoliated-grains are arranged randomly
ex)marble, quartzite
3. Uses
a. buildings, sculptures
b. marble and slate
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4. How it forms -inside Earth
Heat and Magma
Collisions-push rock into earth- toward the
mantle
pressure can change or deform rocks
deep in the earth and with heat- change the
crystal structure- changes the minerals
formed
-new mineral formed
- they are chemically changed
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3.6 Rock Cycle
-Forces deep below earth's surface
plate tectonics
-Forces on surface of earth: mountains,
volcanoes, wind and erosion
-Produces a slow cycle
-that builds, destroys, and changes rocks in
the crust
-slowly changing rocks from one kind to
another
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3.7 Fossil Fuels