Interpreting The Sedimentary Rocks
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2Interpreting the Sedimentary Rocks at ____________________
Step 1: Describe the texture and composition of the clastic (detrital) rocks.
A. Grain/clast size
Rounded grains
Conglomerate
Gravel
Grains >2 mm
Angular grains
Breccia
General term
Sandstone
Grains <2 mm &
Grains mainly quartz
Quartz ss
Sand
visible to naked eye
Grains mainly rock frags
Lithic ss
Grains mainly feldspar
Arkose
Grains not visible to
General term
Mudrock
naked eye
Easily split into thin layers
Shale
Mud
Silt
Grains may be felt between
Siltstone
fingers or across teeth
Clay
Smooth to fingers or across teeth
Claystone
B. Sorting (the range of grain/clast sizes)
C. Shape of grains/clasts (sphericity and roundness)
Spherical
Elongate
D. Sediment maturity
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