Download Igneous Rock Classification Lab

Rock Identification Rock Lab
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Identification of all three rock groups
is based on
TEXTURE and COMPOSITION
the appearance of the
rock
what the rock is made
out of – type of minerals
Igneous Rock Classification
Let’s form an igneous rock
• Two major types of igneous rocks
Intrusive – magma solidifies below the Earth’s
surface
•magma cools very slow
•crystals form interlocking
“mosaic” textures
•very coarse-grained visible
minerals
•referred to as Plutonic rocks
Extrusive – magma solidifies above the Earth’s surface
•magma cools very fast
•minerals can not be seen with un-aided eye
•very fine-grained texture (no visible minerals
•referred to as Volcanic rocks
Igneous Rock Classification
Identification of igneous rocks is based on two main
characteristics
Texture – the appearance of the rock due to the rate of
magma cooling
Composition – the type of minerals found in the rock
(mineral composition)
Textures of Igneous Rocks
Intrusive rocks (Textural terms)
phaneritic texture – crystals are visible and form a
mosaic of interlocking mineral
aggregates (less than 1 cm)
Interlocking crystal grains
phaneritic texture
Extrusive Igneous Rocks (textural terms)
aphanitic texture – crystals are too small to see
See, you really can not see any mineral crystals
glassy texture
• magma cooled extremely fast
(quenched)
• not enough time for atoms to combine
(amorphous solid)- lacks a crystalline
structure
Igneous Rock Classification Lab
Vesicular texture- sponge like appearance, texture contains
numerous cavities or holes
Vesicles – gas bubbles cavities
Pyroclastic texture – textures created by rapidly cooling lava that is
“hurled” through the air picking up fragments
(tuffaceous texture)
rock fragments – pieces of rock “incorporated” into the
rock (tuffaceous)
Igneous Rock Classification Lab
Igneous Rock Composition
mineral composition = mineral assemblages= chemistry
The mineral is either ferromagnesian (dark colored)
or felsic (light colored
ferromagnesian (mafic)
Pyroxene
(Augite)
minerals rich in Fe, Mg – creates a dark colored rocks
Amphibole (hornblende)
Mica - Biotite
Igneous Rock Classification Lab
Igneous Rock Composition
Mineral composition = Mineral assemblages = Chemistry
The mineral is either ferromagnesian (dark colored)
or felsic (light colored)
Felsic – mineral composition is light colored minerals
Ca-plagioclase
K-feldspar (orthoclase)
Mica- muscovite
Quartz
Felsic
40%
Glassy – non-crystalline, non-granular
Color varies between black and brown
Diorite
Gabbro
Peridotite
Andesite
Basalt
Composed of fragments of all sizes
Produced in volcanic environments, Ash
Partially re-fused or cemented
Granodiorite
Highly vesicular, finely crystalline to glassy
Pumice (light), Scoria (dark)
Fine to very fine grains, usually to small
to be distinguished with the unaided
eye or even with a hand lens
Dacite
A mosaic of coarse-grains that are
easily visible to the unaided eye – grains
greater than 1 mm
Mafic
Pegmatite
Granite
Pegmatite
Granite
Very coarse crystal grains, usually all
grains are approximately the same size
w/ respect to each other. Grains> one inch
Rhyolite
Very
Coarse
20%
Glassy Aphan- Phaneitic
ritic
Rock Descriptions
Porous
Texture
Mafic
80%
Fragmental
Extrusive
Intrusive
Origin
Igneous Rock Classification
X
Obsidian
Pumice
Rhyolitic
Tuff
Scoria
Basaltic
Tuff
Sedimentary Rock Identification Lab
Sandstone Arches
How is a sedimentary Rock formed???
Why is the earth’s surface 75% sedimentary rocks?????????
Erosion
Pre-existing
Rock
Sediment
Water, Wind,
Ice
Breaks down
Pre-existing rock
Rivers
Lakes
Lithified
Transported
Compacted
Cemented
Sedimentary
Rock
Three major categories of Sedimentary Rocks
Clastic Sedimentary rocks
Chemical Sedimentary rocks
Bio-chemical (bio-clastic) Sedimentary rocks
Clastic (inorganic-detrital)
rocks are composed of particles or grains. Rock
name is dependent on grain size.
2+ mm
2 mm
1/16 mm
1/256 mm
Chemical Rocks –
inorganic, non-clastic rocks that are commonly
the result of evaporation and precipitation
Chemical rocks contain no fossils, or biological material but may
react with HCl
The Great Salt Lake, Utah
halite (salt) crystals
Calcium Carbonate (CaCO3) chemical rocks
(evaporation / precipitation processes)
Chemically precipitated SiO2
Bio-chemical (bio-clastic, biogenic) rocks –
result from animal and plant secretions. The term clastic
indicates that these rocks contain fossils or parts of plants
shells, compacted plat material
Animal parts
Cemented shell fragments
Lithified plant material
Classification Procedure
Step 1: Determine if the rock is clastic or non-clastic
Step 2: If the rock is clastic, determine the grain size and
diagnostic properties. Make the ID.
Step 3: If the rock is not clastic, determine if the rock is
either chemical or bioclastic
chemical – will not contain particles such as grains and
organic material. Test rock to observe
fizzing (carbonates) Match diagnostic
properties on chart for ID
bio-clastic- rock will be composed of particles that are
organic- animal parts, plant secretions.
Test rock to observe fizzing (carbonate)
Match diagnostic properties on chart for ID
Metamorphic Rocks
Meta (to change) morphic (form) = to change form
Metamorphism– to change a rocks compositional and textural
characteristics by subjecting the rock to
various pressure/temperature relationships
Rocks undergo a solid-state-transformation
The parent rock: represents the pre-existing rock
metamorphism
Example: Shale (parent)
Limestone (parent)
Schist
Marble
Identification of Metamorphic Rocks
Identified by using the rocks Texture and Composition
Compositional characteristics – types of mineral present
common minerals: quartz, feldspar, muscovite
special minerals: talc, garnet, chlorite
related to P/T relationships
Textural characteristics – minerals are oriented in various
degrees of “parallelism”
platy
sub-parallel
paralle
Grain size distribution – fine-grain to coarse-grain
reflects P/T relationships
fine-grain
coarse-grain
Low P/T
High P/T
Gneissic
Alternating light
and dark mineral
bands
Coarse-grained
High P/T
Schistose
Parallel to sub-parallel
Mineral alignment
Slaty
“compressed”
layering - platy
Fine-grained
Low P/T
Textural characteristics
Non-foliated texture – minerals are not visible and there
orientation does not exist
Rock is composed of single type
chemistry.
Example: rocks composed of CaCO3
rocks composed of SiO2
Shows NO foliation
Composed of ONE COMPOSITION
Quartz
SiO2
How can one
Tell the
Difference ?
“Fussed glass”
Scratches glass
Hard H = 7
Plant Material
C -carbon
Calcite
CaCO3
“Sometimes xln”
Fizzes in HCl
Soft H = 3
Classification Procedure
Step 1:
•Determine if the rock is foliated or non-foliated
•does the rock contain “parallelism” or grains
•does the rock consist of a single chemistry with
no visible grains?
Step 2:
•If the rock is foliated
•examine the degree of “parallelism”
•examine the grain-size distribution
•refer to charts for ID
Step 3:
•If the rock is non-foliated
•determine the composition of the rock
•determine the special characteristics
•Refer to charts for ID