Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Day 2
Sedimentary Rock Identification
Sedimentary Rocks
Sedimentary rocks are rocks composed of sediment. Sediment is deposited in a number of
environments of deposition, by both moving air and moving water. Sedimentary rock identification
is primarily based on composition. Texture will still be used but in a different sense than for
igneous rocks.
Texture
Texture of sedimentary rocks in this lab will be taken to indicate origin or type of sediment found
in the rock. Three types of "texture" will be used - clastic, chemical, and biologic.
Clastic Rocks
Clastic sedimentary rocks contain clasts. These are fragments or pieces of rock or minerals. The
composition of clastic sedimentary rocks is divided into three types - clay/silt, sand and gravel.
Clay and silt are less than 1/16 mm. These are not visible to the unaided eye. Sand is clasts
between 1/16 and 2 mm in size, and gravel is greater than 2 mm.
Chemical Rocks
Chemical sedimentary rocks are identified by identifying the mineral from which they are
composed. In this lab there are four minerals that need to be identified - quartz, halite, gypsum
and calcite. Quartz has a hardness of 7 and is very difficult to scratch, even with a good quality
knife blade. Gypsum is relatively soft (Hardness =2) and can be scratched easily with a fingernail.
Halite is common table salt and is most easily identified by taste. However, this is not a sensible
practice in a large lab with many different people handling the samples. Halite has a hardness of
2.5 and cannot be scratched by a fingernail (unpolished fingernail). Calcite readily reacts with a
small drop of HCl.
Biologic Rocks
Biologic sedimentary rocks are which form as the result of the accumulation of organic material or
biologic activity. Coal is usually obvious to most students even though few people seem to have
ever actually examined it up close. The dark brown to black color is the most obvious
charateristic. Coquina and limestone are both composed of calcite . Coquina is composed almost
entirely of shell or fossil fragments. Limestone may or may not contain fossils fragments. Both will
react to HCl. Limestone containing fossils is referred to as fossiliferous limestone.
1
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Sedimentary Rock Identification Chart
TEXTURE
Clastic
GRAIN
SIZE
COMPOSITION
ROCK NAME
>2 mm
rounded quartz, feldspar and rock fragments
Conglomerate
>2 mm
angular quartz, feldspar and rock fragments
Breccia
1/16 - 2 mm
quartz, feldspar
Sandstone
>1/16 mm
feldspar, quartz
Arkose
<1/16 mm
quartz, clay minerals
Siltstone
(Mudstone, Shale)
<1/256 mm
quartz, clay minerals
Claystone
silica (quartz)
Chert
dolomite
Dolostone
calcite
Limestone
halite
Rock Salt
gypsum
Rock Gypsum
silica (quartz)
Chert
loosely compacted organic material and plant
fragments
Peat
densely compacted organic material and plant
fragments
Bituminous Coal
calcite
Limestone
calcite, micro-skeletal fragments
Chalk
calcite, almost entirely shell and skeletal
fragments
Coquina
calcite with some shell and skeletal fragments
Fossiliferous
Limestone
dolomite with some shell and skeletal
fragments
Fossiliferous
Dolostone
Chemical
Biologic
Select a Sample to Identify:
1 2 3 4 5 6 7 8 9 10 11 12
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2
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Directions: For samples 1 -12 list the texture, grain size, composition and rock type
Sample 1
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 2
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 3
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 4
Texture
Grain Size
Composition
Rock Type
Name of
Rock
3
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Sample 5
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 6
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 7
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 8
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 9
Texture
Grain Size
Composition
Rock Type
Name of
Rock
\
4
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Sample 10
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 11
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Sample 12
Texture
Grain Size
Composition
Rock Type
Name of
Rock
Conclusion Question: What did you learn about sedimentary rock that you did not know before?
5
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Day 3
Igneous Rock Identification
Igneous Rocks
Igneous rocks are rocks which solidify from molten material (magma). Cooling of the
magma can occur beneath the surface (plutonic) or on the surface (volcanic). Igneous rocks
can be identified by the determination of the composition and texture of the rock. Once
these two characteristics have been identified, the Igneous Rock Identification chart is used
to identify the rock name.
Igneous Rock Identification Chart
COMPOSITION
Felsic
Intermediate Mafic
Ultramafic
TEXTURE
Pegmatitic
Granite Pegmatite Diorite Pegmatite Gabbro Pegmatite
Phaneritic
Granite
Diorite
Gabbro
Aphanitic
Rhyolite
Andesite
Basalt
Porphyritic
Rhyolite
Andesite
Basalt
Glassy
Vesicular
Pyroclastic
Obsidian
Pumice
Dunite
Basaltic Glass
Scoria
Volcanic Tuff
Composition
Composition of igneous rocks is properly identified by determination of the rock's chemical
composition. This, however, requires chemical equipment and apparatus that is unavailable in this lab.
Fortunately determination of the exact chemical composition is not necessary. Color is often an
indicator of the composition of a rock or mineral and can be effectively used to identify the composition
of most igneous rocks. Light colors, including white, light gray, tan and pink, indicate a felsic
composition. Felsic compositions are rich in silica (SiO2). Dark colors, such as black and dark brown,
indicate a mafic or ultramafic composition. Mafic compositions are poor in silica, but rich in iron (Fe)
and magnesium (Mg). Intermediate compositions have an intermediate color, often gray or consisting
of equal parts of dark and light mineral . Beware that even though an igneous rock may have a felsic
composition (light color), the rock can contain dark colored minerals. Mafic rocks may contain light
colored minerals as well. As mentioned above, the composition of most igneous rocks can be identified
using this system, formally known as the Color Index. However, there are exceptions. The two most
notable are obsidian and dunite. Obsidian is volcanic glass which erupts as a lava flow. Most
obsidian is felsic in composition, yet typically it will have a very dark color (dark brown to black).
Dunite has an ultramafic composition yet is apple green to yellowish green in color. Dunite is
composed almost entirely of the mineral olivine which usually contains both iron and magnesium.
6
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Texture
The texture of an igneous rock does not refer to the roughness or smoothness of the surface.
Textures are based primarily on crystal size. Pegmatitic texture is composed of very large crystals
(larger than 2-3 cm). Phaneritic texture is composed of crystals which are large enough to see but
smaller than pegmatitic texture, and the entire rock is composed of crystals. Aphanitic texture is a
fine grained texture but the crystals are too small to see. Porphyritic texture is composed of crystals
of two different sizes. Typically the large crystals (phenocrysts) are visible while the smaller crystal
are not (referred to as groundmass). Glassy texture is the most readily recognized. The rock is
composed entirely of glass. Few, if any, crystals will be visible. Vesicular texture is formed when
lava solidifies before gases are able to escape. The result is a "bubbly" appearance. Lastly,
pyroclastic texture is composed of volcanic fragments. These fragments or clasts can be very fine
(ash) or coarse (lapilli) or very coarse (bombs and blocks).
Sample Identification
On each of the following pages you will find an image of a rock and a Igneous Rock Identification
Chart. Identify the composition by identifying the color and determine the texture by examining
the crystal sizes that are present. Once this is done the rock name is easily determined using the
Classification of Igneous Rock chart. Click each answer, then check to see if you have correctly
identified the rock sample.
Select a Sample to Identify:
1 2 3 4 5 6 7 8 9 10 11 12
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•
•
•
•
•
•
•
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7
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Directions: For samples 1 -12 list the texture, composition and rock type
Sample 1
Texture
Sample 2
Texture
Sample 3
Sample 4
Composition
Rock Type
Name of
Rock
Composition
Rock Type
Name of
Rock
Texture
Composition
Rock Type
Name of
Rock
Texture
Composition
Rock Type
Name of
Rock
8
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Sample 5
Texture
Composition
Rock Type
Name of
Rock
Sample 6
Texture
Composition
Rock Type
Name of
Rock
Sample 7
Texture
Composition
Rock Type
Name of
Rock
Sample 8
Texture
Composition
Rock Type
Name of
Rock
Sample 9
Texture
Composition
Rock Type
Name of
Rock
\
9
Website: http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/
http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/igneous/
Website can also be found via APES website under “links”
Sample 10
Texture
Composition
Rock Type
Name of
Rock
Sample 11
Texture
Composition
Rock Type
Name of
Rock
Sample 12
Texture
Composition
Rock Type
Name of
Rock
Conclusion Question: What did you learn about igneous rock that you did not know before?
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