ROCKS
MINERAL MIXTURES
THE ROCK CYCLE
METAMORPHIC
IGNEOUS
SEDIMENTARY
Melting
Sedimentary
Process
Sedimentary
Process
Metamorphism
MAGMA
Metamorphism
Metamorphism
Cooling & Crystallization
Sedimentary
Process
ENDURING UNDERSTANDINGS
Rocks reveal the expanse of geologic time, the composition of Earth's crust and the forces that shape it, past
life and environments, even the composition of other planets and the age and formation of the universe.
The Rock Cycle relates the formation of each rock type to the others as a continuous cycle of creation and
alteration.
The three main rock types are igneous, sedimentary and metamorphic.
What is a rock?
A rock is a solid combination of one or more minerals.
All rocks begin as magma.
IGNEOUS ROCK
When magma cools and crystallizes, igneous rock is formed. The rate that magma cools determines the size
of the crystals, or the "texture", of igneous rock.
Igneous rocks are classified according to their texture & composition.
If the magma cools within the crust where it is
insulated, it takes a very long time to crystallize.
This allows time for the mineral crystals to grow very large. An igneous rock with
very large crystals is
said to have pegmatitic or phaneritic texture.
If magma reaches the surface, it cools very quickly. This does not give time
for crystals to grow large so they remain very small. An igneous rock with
microscopic-sized crystals has aphanitic texture.
If magma begins to cool slowly below the surface but then is uplifted to finish
cooling quickly, it will have a combination of large and microscopic crystals, and
the rock is said to have a porphyritic texture.
If magma cools extremely quickly, as when it erupts into
water, there is no time for crystals to grow and the rock is
said to have amorphous texture.
When magma with a lot of gas cools, gas is trapped within the rock, creating a vesicular
texture.
When very hot ash falls to the ground, it "welds" into a rock with pyroclastic
texture.
It is very light-weight, being made of a volcanic "spun glass".
ENVIRONMENTS FOR THE FORMATION OF IGNEOUS ROCK
IGNEOUS ROCK COMPOSITION
Igneous rock composition depends on the minerals that make up the rock.
Felsic igneous rocks are rich in feldspar, quartz, and other low density minerals, and
are very low in minerals with low melting points like iron and magnesium. Felsic
igneous rocks are generally light in color.
Mafic igneous rocks are rich in iron, magnesium and higher density minerals
with high melting points, and poorer in silicate minerals. Mafic igneous rocks
are darker in color than felsic rocks.
BOWEN'S REACTION SERIES
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IGNEOUS ROCK CROSSWORD
SEDIMENTARY ROCK
Sedimentary rocks are classified by how they were formed, as either clasic or nonclastic.
CLASTIC SEDIMENTARY ROCKS are formed by the weathering of pre-existing rocks
into sediments and the transportation, deposition and lithification of the sediments.
1.
Weathering is the breaking down of large rocks into smaller pieces, or "clasts", by ice,
running water, wind or biological activity.
2. Transportation is the moving of sediments
by running water, glaciers, winds or gravity.
3. Deposition occurs when the transporting agent
loses energy and drops the sediment it is carrying.
Sediment size
by energy in
depositional
environment
4. Over time, lithification occurs due to compaction, cementation or both.
THE FORMATION OF COAL
NONCLASTIC SEDIMENTARY ROCKS
are formed either chemically or biologically.
Chemically-formed rocks
Formed by precipitation of minerals from water onto the sea floor due to oversaturation of that
mineral or change in the water temperature.
Chert is formed by the precipitation of silica
out of seawater.
Evaporites form when sea water evaporates.
Carbonates are the most widespread
sedimentary rocks, especially limestone, and
can form layers hundreds of feet thick.
Biologically-formed rocks
form from the activities or the remains of living organisms.
Sedimentary rock that is at least 30% mega fossils is called fossiliferous limestone.
Rock that is 90% mega fossils is called coquina.
In the deep ocean, microscopic organisms called foraminifera with calcareous shells, die and their remains filter to the bottom
forming layers of ooze that turns to limestone.
Chert can be formed from the remains of
micro-organisms called radiolarians or
diatoms.
Chalk is formed from the remains of microorganisms called cocolithophorids.
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SEDIMENTARY ROCKS CROSSWORD
METAMORPHIC ROCK
Metamorphic rocks are formed from pre-existing rocks by intense heat and pressure or by chemical alteration.
Metamorphism is Greek for "changed form".
Metamorphic rocks can relate the intensities, ages and types of metamorphism that have occurred over geologic time.
TYPES OF METAMORPHIC ROCKS
Foliated metamorphic rocks
are formed by intense pressure
as from mountain-building.
In foliated metamorphic rocks,
partial melting from intense
pressure forces the mineral
crystals to align in the same
direction as layers, or "foliations".
Nonfoliated metamorphic rocks
are formed by intense heat as
within the Earth, or by chemical
alteration.
In nonfoliated metamorphic rock, intense heat causes
partial melting allowing the minerals crystals to grow
very large and "weld" together, creating a very hard
rock.
Slate - crystals aligned flat
Foliated Metamorphic Rocks result when intense
pressure causes existing rock to partially melt and fold.
When the pressure is released, these "plastic" rocks
record the intensity of the pressure.
and parallel; small grained
rocks
Phyllite - slightly polished
luster; medium thick layers
and crystal size
Schist - mineral crystals
align in parallel planes;
large crystals; sparkly
luster
Gneiss - minerals separate
into compositional layers;
coarse grained, highest
metamorphic grade before
melting
TYPES OF METAMORPHISM
Regional Metamorphism occurs over a very large area.
Mountain building from tectonic forces create foliated rocks due to directed pressure.
Burial metamorphism creates nonfoliated rocks due to equal pressure from all directions.
Contact metamorphism - very localized
Heat from plutons or under lava flows alters country rock.
Metasomatism - magmatic fluids seep into country rocks, combine to form new
minerals; escaping gasses carry ions, forming ore deposits.
Hydrothermal - water seeps through cracks near
a shallow pluton, is super-heated
and dissolves minerals from
surrounding rocks; carries
dissolved minerals and deposits
on surface.
Shock - impact produces brief, ultra-high pressure,
causing broken crystal structures and
high-pressure polymorphs.
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METAMORPHIC ROCKS CROSSWORD
ROCK IDENTIFICATION GRAPHIC ORGANIZER