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Rocks
and
Minerals
8 September 2014
Rocks and Minerals: Definitions
– A mineral is solid inorganic material of the Earth that
has both a known chemical composition and a
crystalline structure that is unique to that mineral
– A rock is a solid aggregate of one or more minerals that
have been cohesively brought together by a rockforming process.
Earth Interior: Physical
Minerals
the building blocks of rocks
Mineral Characteristics
• natural
• inorganic
• solid
• definite composition
• crystal structure
Mineral Composition
Minerals are grouped or classified based on
their composition. There are 6 groups
1. Carbonates - contain
carbon, oxygen, and one
ore more metallic element
2. Silicates
- formed from silicon and
oxygen
- elements combined to
form a silicon
tetrahedron, 1 silicon
atom and 4 oxygen atoms
- formed from cooling
magma
- either near the surface
(few crystals) or deep
below surface (larger
crystals)
3. Oxides
- Minerals that
contain oxygen and
one or more other
element(s)
Gypsum
4. Sulfates and
Sulfides
- Minerals containing
sulfur
Pyrite
5. Halides
-minerals containing
halogen ions plus
one or more other
elements
Halite
6. Native Elements
Minerals that exist in
a relatively pure
form
i.e. Gold, silver,
copper
Gold crystal structure
Rocks
– Elements are chemically combined to form minerals
– Minerals are physically combined to form rocks.
Igneous Rocks
• Magma- molten material underground
• Lava- magma that reaches the surface
• Igneous rocks are formed from magma that
has cooled and hardened either beneath the
surface or from a volcanic eruption
2 Ways to Form Igneous Rock
• Intrusive Igneous
Rocks- form when
magma hardens
beneath Earth’s
surface
• Magma intrudes into
existing rocks
• Extrusive Igneous
Rocks- form when
lava hardens on the
surface of the Earth
• Extruded onto the
surface
rhyolite
granite
• Magma contains some gases, including
water vapor- this make it less dense, so it
rises
• As magma rises, it cools and forms crystals
• The longer the cooling time the larger the
crystals
• Granitic Composition- contain
mainly quartz and feldspar,
some with biotite mica and
amphibole. Make up major
rocks of continental crust
• Basaltic Composition- contain
mainly dark colored minerals
and feldspar, along with Mg
and Fe. Darker and denser than
granitic composition
Igneous rock classification scheme based on mineral
composition and texture. There are other blends of minerals
with various textures, many of which have specific names.
Granite is a coarse-grained igneous rock composed mostly
of light-colored, light-density, nonferromagnesian minerals.
The earth's continental areas are dominated by granite and
by rocks with the same mineral composition of granite.
This is a piece of obsidian, which has the same chemical
composition as the granite. Obsidian has a different texture
because it does not have crystals and is a volcanic glass. The
curved fracture surface is common in noncrystalline
substances such as glass.
Sedimentary Rocks- formed from
compacted and cemented sediments
• Weathering physically and chemically
breaks rocks into small pieces called
sediments
• Sediments are moved
by wind, water, ice,
and gravity
• Eventually, they are
dropped and form layers
that are cemented together
Weathering, Erosion, and
Deposition
• Weathering breaks
rocks down
• Erosion involves
weather and the
removal of rock
• Deposition is the
dropping of sediments
• Sediments are
deposited according to
size
Compaction and Cementation
• Compaction is the
process that squeezes
the water out of the
sediments. It is caused
by the weight of the
sediments.
• Cementation takes
place when dissolved
minerals are deposited
in the tiny spaces among
the sediments.
• Cementing holds the
sediments together.
Classification of Sedimentary
Rocks- based on formation
• Clastic Sedimentary
• Chemical
Rocks are formed
Sedimentary Rocks
from weathered bits of
are formed when
rocks and minerals
dissolved minerals
precipitate from water
• Grouped according to
solution
size of the sediments
Coquina
in the rock
limestone
• Sedimentary rocks hold many clues to the
Earth’s history
• Layers of sediments are records of geologic
events on Earth
• Fossils are unique to sedimentary rocks
This is a sample of breccia, a coarse-grained
sedimentary rock with coarse, angular fragments.
Compare the grain sizes to the centimeter scale.
This is a sample of sandstone, a sedimentary rock that
formed from sand grains in a matrix of very fine-grained
silt, clay, or other materials. The grains in this sample are
mostly the feldspar and quartz minerals, which probably
accumulated near the granite from which they were eroded.
This is a sample of limestone, a sedimentary rock made of
calcium carbonate that formed under water directly or
indirectly from the actions of plants and animals. This finegrained limestone formed indirectly from the remains of
tiny marine organisms.
Metamorphic Rocks- form when
existing rocks undergo change through
heat and pressure
• Metamorphism means
to change
• Most metamorphic
changes occur at high
temperatures and
pressure
• These occur deep
below the Earth’s
surface and extend
into the mantle
Agents of Metamorphism
• Heat- causes existing
minerals to
recrystallize or new
minerals to form
• Pressure- causes the
spaces between
mineral grains to
close= more compact
rock= greater density
Increasing metamorphic change occurs with
increasing temperatures and pressures. If the melting
point is reached, the change is no longer
metamorphic, and igneous rocks are formed.
This is a sample of marble, a coarse-grained metamorphic
rock with interlocking calcite crystals. The calcite crystals
were recrystallized from limestone during metamorphism.
Rock Cycle
• Earth is a dynamic planet with the surface
and interior in a constant state of flux.
– Internal changes alter the surface by moving the
Earth’s plates, building mountains.
– Seas advance and retreat over the continents
brining in new materials and taking other
materials away.
– Rocks are continually being changed by Earth’s
forces
A schematic diagram of the rock cycle concept,
which states that geologic processes act
continuously to produce new rocks from old ones.
The Rock Cycle
Planetary History
• Planets formed hot: Energy from collisions,
radioactivity
• Heavier materials dropped to center: metals
at core; basic, mafic rocks in mantle; lighter
float to top (differentiation)
• Radioactive heating declines; crust
solidifies
• Tectonics, impacts, volcanism, erosion
modify surfaces (next lectures)