Lab Report, Sedimentary Rocks
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Laramie County Community College *
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Course
1100
Subject
Geology
Date
Dec 6, 2023
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docx
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GEOL 1100 500
Lab Report, Sedimentary Rocks
Pre-Lab
Use your textbook and other sources or websites to answer the questions below. Answer the questions as carefully as possible. Remember, when you are finished, it will be assumed that you understand the material that is covered in this exercise. Please use a bright blue font to indicate your answers.
1.
The two ways in which rocks are weathered into sediment are. ______
Mechanical
____ and ______
Chemical
_________________. 2.
Having rocks broken into smaller and smaller pieces provides more ___
Surface area
_ for chemical attack.
3.
_
Chemical
_____ weathering changes the internal structure of the minerals.
4.
What mineral is very resistant to erosion? Where some places it is commonly found? Quartz, commonly found in soil, rivers, and on beaches. Found in sandstones. 5.
Sediment becomes rock through ___
Lithification
___ and __
Precipitation
___.
6.
Clastic sedimentary rock textures are described in terms of __
grain size, grain shape, and grain shorting
__.
7.
Chemical sedimentary rocks are formed by ___
precipitation and aggregation of minerals from a solution.
8.
In a global sense, the single most characteristic feature of sedimentary rocks is _____
Beds/Horizontal Strata
________. v. SU22
9.
Match the following sedimentary structures to their past geological conditions.
__
a
___ cross-bedding a) flowing water
___
d
__ mudcracks
b) sand dunes
__
b
___ ripple marks
c) swamp
___
c
__ fern fossil
d) alternating wet and dry periods
10. The stronger the water current, the __
larger
__ the particle size that can be carried.
Lab: Sedimentary Rock Descriptions and Identification
Fill in each line. If not applicable, enter N/A. Please use a different color or font to distinguish your answers. Rock G
NAME: Chert
1.
Texture (clastic/chemical/organic): Chemical 2.
Grain size (if visible, in mm): Microcrystalline 3.
Grain shape (if visible): N/A
4.
Reaction with acid: No reaction 5.
Hardness (relative to glass): Scratches Glass
6.
Composition, mineral/grain type: Quartz
7.
Description, color, other features: When a flashlight is shined on it, it sparkles due to crystals. 8.
Possible environment (s) of formation: Lakes or deep sea
Rock H
NAME: Shale/Mudstone
1.
Texture (clastic/chemical/organic): Clastic v. SU22
2.
Grain size (if visible, in mm): < 1/256 mm
3.
Grain shape (if visible): N/A
4.
Reaction with acid: No reaction 5.
Hardness (relative to glass): Soft
6.
Composition, mineral/grain type: Clay/mud
7.
Description, color, other features: It looks like it could contain fossil, split into layers. 8.
Possible environment (s) of formation: Lakes or rivers Rock I
NAME: Fossiliferous Limestone
1.
Texture (clastic/chemical/organic): Biochemical 2.
Grain size (if visible, in mm): Fossils
3.
Grain shape (if visible): Fossils
4.
Reaction with acid: Reacts to acid.
5.
Hardness (relative to glass): Softer than glass
6.
Composition, mineral/grain type: Calcite 7.
Description, color, other features: Shell fragments imprinted, grayish color, vesicular like. 8.
Possible environment (s) of formation: Lake (plant/shell fragments), Shallow Sea, or
reef
Rock J
NAME: Sandstone 1.
Texture (clastic/chemical/organic): Clastic 2.
Grain size (if visible, in mm): 1/16-2mm 3.
Grain shape (if visible): Angular v. SU22
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4.
Reaction with acid: No reaction 5.
Hardness (relative to glass): Soft
6.
Composition, mineral/grain type: Sand
7.
Description, color, other features: Feels a little like sandpaper 8.
Possible environment (s) of formation: Coastal Beaches, Desert, or Rivers Rock K
NAME: Conglomerate
1.
Texture (clastic/chemical/organic): Clastic
2.
Grain size (if visible, in mm): >2mm, visible to naked eye
3.
Grain shape (if visible): Rounded
4.
Reaction with acid: No reaction 5.
Hardness (relative to glass): Softer than glass
6.
Composition, mineral/grain type: Coarse-grained (Gravel) 7.
Description, color, other features: Brownish color with variety of large dark to light brown color grains. There is what looks like old mass on side of rock. 8.
Possible environment (s) of formation: (
Needs strong water) mountain stream or alluvial fan environments.
Rock L
NAME: Rock Gypsum
1.
Texture (clastic/chemical/organic): Chemical
2.
Grain size (if visible, in mm): Crystalline 3.
Grain shape (if visible): N/A
4.
Reaction with acid: No reaction 5.
Hardness (relative to glass): Very soft v. SU22
6.
Composition, mineral/grain type: Gypsum 7.
Description, color, other features: White, smooth
8.
Possible environment (s) of formation: Lakes
Application Questions: (refer to Chapter 5 and the Sedimentary Environments diagram for help).
Based on the physical characteristics of each rock, determine the most likely environment(s) in which it formed. Write these is number 8 for each rock. Lab Reflection: One of the key concepts that I took away from this lab is that the grain size can interfere a lot about a rock. If a rock has a size of 2mm or more, it will most likely be conglomerate or breccia. Between 2mm to 1/16 mm is likely to be sandstone. Between 1/16 to 1/256mm likely slit or mud. Lastly less than 1/256mm is going to be a mudstone. This is if the rock is a clastic sedimentary rock. If not, the grain will either be fossils or crystalline. If it contains fossils, then it is biochemical sedimentary rock. If it is crystalline, it will most likely be chemical sedimentary rock due to recrystallization (growing of new crystals at the expense). By observing this the environment of the rock can be inferred. Clastic rocks will be in deserts, glaciers, rivers, lakes, beaches, deltas, shallow sea, and deep sea. Mud will be in deep sea, rounded sand, well-sorted in shallow seas, poorly sorted,
rounded grains (mud-sand) in deltas, and on the beach well-shorted and well-
rounded grains found here. Cross stratification is common in deserts. They will never be found in reefs because they do not contain shell fragments. However, if it does contain shell fragments(fossils) it can be from lakes, shallow sea, or reefs.
Chemicals are only found in deep sea, shallow sea, and lakes. Crystalline/microcrystalline of halite, gypsum, silica, iron material in lakes. Spherical calcite in shallow seas and microcrystalline of silica in deep sea. A pattern I observed was that all the rocks except for one (chert) were not able to scratch glass. This is because chert contains quartz while the rest contains generally soft minerals. A challenge for me was distinguishing sandstone and mudstone. I made the decision based on the fact that one of the rocks was layered like a mudstone whereas the other did not have layers. I found it surprising that conglomerate could not scratch glass. I found this interesting because it felt hard to me. v. SU22
v. SU22
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Instructor’s Grading Rubric:
Superior
Developing
Lacking
Pre-lab
Mostly correct answers. 8-10 points
Some errors or omissions, and/or indication that instructions were not followed.
6-8 points
Incomplete and/or there are multiple errors.
0-5
Rock Descriptions and Identification
All 10 identification sections are complete and logical, with
minimal errors; answers are recorded for all 6 diagnostics, the “other features” when appropriate, and a rock name is recorded
15-20 points
Some errors or omissions, and/or indication that instructions were not followed.
10-6 points
Incomplete and/or there are multiple errors.
0-5 points
Applications
Questions
Mostly correct answers. 8-10 points
Some errors or omissions, and/or indication that instructions were not followed.
6-8 points
Incomplete and/or there are multiple errors.
0-5
Reflection
Thoughtful reflection on any problems encountered, interesting discoveries, etc.
10 points
Reflection is lacking in detail.
5-9 points
Minimal or no reflection.
0-4 points
TOTAL: /50
v. SU22