1. Rock Identification Rock Lab1

2. Identification of all three rock groups is based on
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
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

4. Textures of Igneous 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

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. Texture Origin Intrusive Extrusive X 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. Grains> one inch
Coarse
Very
Granite
Pegmatite
Mafic
Pegmatite
Intrusive
A mosaic of coarse-grains that are
easily visible to the unaided eye – grains
greater than 1 mm
Phane-
ritic
Grano-
diorite
Diorite
Gabbro
Peridotite
Granite
Aphan-
itic
Fine to very fine grains, usually to small
to be distinguished with the unaided
eye or even with a hand lens
Rhyolite
Dacite X
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
Rhyolitic
Tuff
Basaltic
Tuff
mental
Frag-

10. Sedimentary Rock Identification Lab
Sandstone Arches

11. 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
Deposited
Transported
Lakes
Lithified
Compacted
Cemented
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
Rocks undergo a solid-state-transformation
The parent rock: represents the pre-existing rock
metamorphism
Example: Shale (parent) Schist
Limestone (parent) Marble 17

18. FOLIATED 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 18

19. Slaty Schistose Gneissic Fine-grained Coarse-grained Low P/T High P/T
“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. NON-FOLIATED 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 20

21. How can one Tell the Difference ?
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 22

25. phanaritic porphyritic clastic glassy pyroclastic vesicular
foliated tuffaceous
chemical
aphanitic
bio-chemical
I = igneous S = sedimentary M = metamorphic