Igneous Rock Classification Lab

1
Rock Identification Rock Lab
2
Love it, Learn it, Live it , be one with it!
Identification of all three rock groups is based
on TEXTURE and COMPOSITION
what the rock is made out of type of minerals
the appearance of the rock
3
Igneous Rock Classification

• Lets form an igneous rock
• Two major types of igneous rocks

• Intrusive magma solidifies below the Earths
  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 Earths
  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

4

• 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
5
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

6
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)
7
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)
• minerals rich in Fe, Mg creates a dark
  colored rocks

Pyroxene (Augite)
Amphibole (hornblende)
Mica - Biotite
8
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
9
Igneous Rock Classification
Felsic
Mafic
80
Origin
Texture
40
20
Rock Descriptions
Very coarse crystal grains, usually all grains
are approximately the same size w/ respect to
each other. Grainsgt one inch
Very Coarse
Mafic Pegmatite
Granite Pegmatite
Intrusive
A mosaic of coarse-grains that are easily visible
to the unaided eye grains greater than 1 mm
Grano- diorite
Phane- ritic
Peridotite
Gabbro
Diorite
Granite
Fine to very fine grains, usually to small to be
distinguished with the unaided eye or even with a
hand lens
Aphan- itic
X
Rhyolite
Dacite
Andesite
Basalt
Glassy
Glassy non-crystalline, non-granular Color
varies between black and brown
Obsidian
Extrusive
Por- ous
Highly vesicular, finely crystalline to
glassy Pumice (light), Scoria (dark)
Pumice
Scoria
Composed of fragments of all sizes Produced in
volcanic environments, Ash Partially re-fused or
cemented
Basaltic Tuff
Rhyolitic Tuff
Frag- mental
10
Sedimentary Rock Identification Lab
Sandstone Arches
11
How is a sedimentary Rock formed???
Why is the earths surface 75 sedimentary
rocks?????????
Erosion
Sediment
Pre-existing Rock
Water, Wind, Ice
Breaks down Pre-existing rock
Rivers
Deposited
Transported
Lakes
Compacted Cemented
Lithified
Sedimentary Rock
12
Three major categories of Sedimentary
Rocks Clastic Sedimentary rocks Chemical
Sedimentary rocks Bio-chemical (bio-clastic)
Sedimentary rocks
13
Clastic (inorganic-detrital) rocks are composed
of particles or grains. Rock name is dependent
on grain size.
Decreasing grain size
2 mm
2 mm
1/16 mm
1/256 mm
14
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
15
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
16
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
17
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 Rock
s undergo a solid-state-transformation
The parent rock represents the pre-existing rock
metamorphism Example
Shale (parent) Schist
Limestone (parent) Marble
18
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 parallel
FOLIATED
Grain size distribution fine-grain to
coarse-grain
reflects P/T relationships fine-grain
coarse-grain Low P/T
High P/T
19
Slaty
Schistose
Gneissic
compressed layering - platy
Parallel to sub-parallel Mineral alignment
Alternating light and dark mineral bands
Fine-grained Low P/T
Coarse-grained High P/T
20
Textural characteristics
Non-foliated texture minerals are not visible
and there
orientation does not exist
Rock is composed of single type
chemistry.
NON-FOLIATED
Example rocks composed of CaCO3
rocks composed of SiO2
21
Shows NO foliation Composed of ONE COMPOSITION
How can one Tell the Difference ?
Quartz SiO2
Calcite CaCO3
Fussed glass Scratches glass Hard H 7
Sometimes xln Fizzes in HCl Soft H 3
Plant Material C -carbon
22
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