Transcript Minerals and Rocks

Minerals and Rocks
Ch 6
8th grade
6.1 Vocabulary
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Inorganic
Crystal
Streak
Luster
Cleavage
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Fracture
Geode
Crystallization
Solution
Vein
What is a Mineral?
• A mineral is a naturally occurring solid that
can form by inorganic processes and that
has a crystal structure and a definite
chemical composition.
• A substance must have all 5 to be a
mineral.
•Naturally occurring: formed by nature
•Solid: definite volume and shape
•Inorganic processes: not formed from
organisms
•Crystal structure: particles line up in a
repeating pattern
•Definite chemical composition: always
contains certain elements in specific ratio
How are Minerals Identified?
• Color: only a few minerals have their own
characteristic color.
• Streak: does not vary, and often is not the
same as the color
• Luster
• Hardness: most useful characteristic, Mohs
hardness scale assigns a ranking 1 (talc) to
10 (diamond); determined by a scratch test:
mineral scratches a softer mineral and will
be scratched by a harder mineral
• Density: no matter the size of a sample, the
density remains the same; a balance
determines the mass and water
displacements determines the volume:
• Density= mass/volume
• Crystal structure: all crystals of a mineral
have same structure; light bounced off a
small crystal will produce distinct patterns;
crystals are classified by number of faces
(sides) and the measure of the angles at
which the faces meet.
• Cleavage and Fracture: cleavage is
determined by the arrangement of atoms;
otherwise, the characteristic type of
fracture is seen
• Special Properties: some minerals may
bend light; conduct electricity, glow under
UV light; or are magnetic
How do Minerals Form?
1. Some minerals form from organic
processes.
2. When elements and compounds that are
dissolved in water leave a solution,
crystallization occurs.
– Some minerals form when solutions evaporate.
– When hot water dissolves elements and then
begins to cool, the elements crystallize as
minerals.
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Pure metals that crystallize from hot water solutions
often form veins.
3. Some minerals form when magma and lava
cools. Size of crystals depends upon:
-- amount of gas the magma contains,
-- chemical composition
-- rate at which it cools:
 magma cools slowly so large crystals form
 lava cools quickly creating small crystals.
Magma and lava contains oxygen and silicon that
create silicates that make up a majority of
Earth’s crust
• Earth’s crust is made of common minerals.
• Less common minerals are not found evenly
throughout the crust. These minerals are
deposited in concentrated areas called ores.
• Forming crystals
6.2 Vocabulary
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Rock-forming mineral
Granite
Basalt
Grain
Texture
Three Main Rock Types
How Do Geologist Classify Rocks?
• Mineral composition and color:
– Rocks are made of mixtures of minerals and
other materials and some contain only a single
mineral.
– About 20 minerals make up most of the
Earth’s crust.
– A rock’s color provides clues to its mineral
composition, but does not provide enough
information to identify it.
• Texture:
– Most rocks are made up of grains that give the
rock its texture.
– To describe texture, terms are used based on
size, shape, and grain pattern.
• Size: large grains are easy to see and called coarse
grained while fine-grained rocks have small grains
• Shape: results from the shape of the mineral crystals
or the jagged bits of several rocks
• Pattern: banded rocks with grains that form layers of
colored swirls or nonbanded rocks with no visible
pattern.
• Origin (how the rock forms):
– Igneous: formed from cooling of magma or
lava
– Sedimentary: forms layers of small particles of
rock or remains of organisms that are pressed
and cemented together
– Metamorphic: forms when a rock is changed
from heat, pressure, or by chemical reactions.
• Geology Kitchen: The 3 Types of Rocks
6.3 Vocabulary
• Rock cycle
What is the Rock Cycle?
• Forces deep inside Earth and at the
surface produce a slow cycle that builds,
destroys, and changes the rocks in the
crust.
• While there are many pathways through the
rock cycle, a common one is:
– Granite forms below Earth’s surface as magma
cools (so it’s igneous rock).
– Earth’s forces push the granite upward and
weathering and erosion wear it away into sand
carried to the oceans
– Layers of sand pile up. Either it gets compacted
or cemented by calcite to become sandstone
(now sedimentary rock).
– Pressure builds and silica (from the quartz in the
granite) replaces the calcite. The rock changes
from gritty to smooth: from sandstone to
quartzite (a metamorphic rock).
• The changes of the rock cycle are closely
related to plate tectonics. Plate movements
help drive the rock cycle by helping to form
magma, the source of igneous rock.
• Where oceanic plates move apart, magma
moves upward and fills the gap with new
igneous rock.
• Where an oceanic plate is subducted,
magma forms and rises.
• A collision of plates may push rocks so deep
that they melt to form magma
• The collision of plates can be strong enough
to push up a mountain range. Then
destructive forces begin which leads to the
formation of sedimentary rock.
• A collision of plates can also push rocks
deep down beneath the surface. Heat and
pressure could change the rock into
metamorphic rock.
• As the rock on the Earth moves through the
rock cycle, material is not lost or gained,
simply changed forms.
Rock Cycle
• Rock Cycle Foldable
• Rock Cycle Modeled Out of Crayons