lab 5 (1)
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Dec 6, 2023
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GEOL 1302
Lab 05
Clastic Sedimentary Rocks
The first task in this lab is to make and describe some “clasts”.
Then you are going to
describe and identify some common clastic (or detrital) sedimentary rocks.
Your lab
instructor will summarize the main characteristics of the different rocks.
In the third part of
the lab, you should list some possible environments in which the rocks that you identified
might have formed. Some help to perform the rock identification and information about
clastic sedimentary rocks can be found below.
Please submit both papers to your instructor.
Don’t forget to put your name on the worksheets!
Grain Size:
●
Gravel > 2 mm
●
Sand 0.06-2 mm
●
Silt 0.004-0.06 mm
●
Clay < 0.004 mm
Rounding:
●
Angular
●
Sub-rounded
●
Well-rounded
Sorting:
●
Poorly sorted
●
Well-sorted
Other Observations:
●
Layering
●
Fissility
●
Color
●
…
Identification and Formation:
1
http://geology.about.com/od/rocks/a/Rock-Tables.htm
http://ratw.asu.edu/aboutrocks_clasticsedimentary.html
http://www.earthsci.org/education/teacher/basicgeol/sed/sed.html
2
Clastic Sediment
Use the two pieces of granite provided in the lab and tap them together over a piece of paper.
The broken pieces that fall onto the paper are called “clasts”.
Observe the pieces with a hand
lens.
Are your clasts fragments of crystals or rock fragments (or both)?
they are both crystal and rock fragments
What kinds of sediment did you just make – pyroclastic, siliciclastic, or bioclastic sediment?
Siliciclastic
Sketch at least three of your pieces (at a larger scale).
What is the rounding of these pieces?
Angular
What is/are the size(s) of your pieces?
Use the grain size descriptions given on the first page
of this lab. 2
Coarse-grained = 0.06 – 2mm
What is the sorting of your pieces?
Poorly sorted
3
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Examining and Classifying Clastic Sedimentary Rocks
Sample
Number
Grain Size
Rounding
Sorting
Other Observations
Rock Name
1
Gravel > 2mm
Sub-rounded
Poorly sorted
Sedimentary rock
Clastic
Rounded particles
Conglomerate
2
Clay <0.004 mm
Too small to
see
Sub-angular
Well sorted
Fissile
Sedimentary rock
Laminated
Shale
3
Sand 0.06– 2mm
Well rounded
Well sorted
Light-brown sandy color
Particles are very fine-
grained
Clay-sized particles keep
the layers of sand together
Sandstone
4
Gravel >2mm
Angular
Unsorted
Angular Particles
Grayish color
Breccia
5
Clay <0.004mm
Sub-rounded
Well sorted
Particles too fine to see
Reddish color, might mean
oxidation of Iron
Siltstone
Rocks provided: Breccia, Conglomerate, Sandstone, Shale, Siltstone
4
Clastic Sedimentary Rock Formation
In what environment might the rocks that you identified in the first part of the lab have
formed?
Sample #/Rock Name
Formation/Environment
Conglomerate
Strong water currents like beaches or flowing streams
Shale
Chemical weathering of rocks breaks down to clay material.
muddy material is carried downstream, settles at the bottom
of a lake, ocean, or swap. accumulation could possibly
create shale
Sandstone
Sand is carried by rivers, wind, or waves. Deposited by its
source rock
beaches
Breccia
Commonly formed at the base of an outcrop where
mechanical weathering debris accumulates
Alluvial Fan
siltstone
Any places where a current, wave, or wind accumulates
sand and mud
Old delta or lake
5