Expedition V.1 Lab Sedimentary Rocks Identification - Ana Robles
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Pima Community College *
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Course
GLG-101I
Subject
Geology
Date
Apr 3, 2024
Type
Pages
4
Uploaded by AmbassadorMoonBuffalo52
Rock Properties:
Clastic rocks are made up of fragments of pre-existing rocks and minerals. These fragments,
called clasts, vary in size, shape, and sorting. Clastic rocks can range from fine-grained siltstones to coarse-
grained conglomerates, and their clasts may be angular or rounded.
How they form
: Clastic sedimentary rocks are formed primarily by mechanical weathering and erosion. When
rocks are broken down into smaller particles through processes like abrasion, these particles are transported
by water, wind, or ice and eventually deposited in layers. Over time, compaction and cementation occur,
binding the clasts together to form a rock.
Rock Properties:
Chemical sedimentary rocks are composed of minerals that precipitate from water
saturated with dissolved substances. These rocks are typically made up of a single type of mineral and often
have a crystalline structure.
How they form
: Chemical sedimentary rocks form when minerals in solution, such as calcite or halite,
precipitate out of the water due to changes in environmental conditions, such as evaporation or chemical
reactions. The minerals accumulate over time and solidify into rock.
The two main types or categories of sedimentary rocks are clastic
(or detrital) sedimentary rocks and chemical
sedimentary rocks.
Clastic Sedimentary Rocks:
Chemical Sedimentary Rocks:
Key Difference:
The main difference between these rock types is in their formation processes. Clastic rocks are
made from weathered and transported fragments of pre-existing rocks, while chemical rocks form through the
precipitation of minerals from solution. Clastic rocks have a wide range of clast sizes and shapes, reflecting their
diverse source materials, on the other hand, chemical rocks are typically made of a single mineral type and have
a more uniform appearance.
Ana Robles
Expedition V.1 Lab: Sedimentary Rocks Identification
Part 1
1.) What are the two main types or categories of sedimentary rocks? Explain each in terms of rock properties,
and how those types of sedimentary rocks form. It's important here to be able to explain how/why these rock
types/categories are different.
Ana Robles
Expedition V.1 Lab: Sedimentary Rocks Identification
Part 1
Limestone is a sturdy rock because the individual clasts that make it up are cemented together with
abundant silica.
Sedimentary rocks made up of pre-existing pieces are generally referred to as sandstone, no matter the
size of those pieces. When classifying clastic sedimentary rocks, we pay attention to the shape of the individual clasts, not the
shape of the rock itself.
Chemical sedimentary rocks always involve some biological process to form them, whether it be bacteria
or larger organisms like bivalves. 2.) For each of the statements below, explain how/why it is incorrect. If the statement is correct, just say so.
Incorrect: Limestone is primarily composed of calcium carbonate (CaCO3) minerals, not silica. While silica can be
present in some limestone as impurities or as secondary cement, it is not the primary binding agent in limestone. Incorrect: Sedimentary rocks made up of pre-existing pieces are referred to as clastic rocks, and they are
categorized based on the size of the sediment particles, not automatically classified as sandstone. Clastic rocks
have a range of grain sizes such as sandstone, mudstone, shale, siltstone, and claystone, each with its own
classification based on grain size and other characteristics.
Correct: When classifying clastic sedimentary rocks, geologists focus on the shape and characteristics of the
individual clasts (sediment particles) within the rock. The shape, size, sorting, and rounding of these clasts are
essential for classification.
Incorrect: Not all chemical rocks need life. Some form just from chemicals and water, without any help from
living things.
Ana Robles
Expedition V.1 Lab: Sedimentary Rocks Identification
Part 2
5 Sedimentary Rocks from my Kit
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Ana Robles
Expedition V.1 Lab: Sedimentary Rocks Identification
Part 3
5 Sedimentary Rocks from my Kit
A clastic sedimentary rock with sand-sized clasts.
A clastic sedimentary rock with well-sorted clasts.
A chemical sedimentary rock formed through the evaporation of mineral-rich water.
To figure out it's shale, I looked at the fine grain size and the way it can easily break into
those thin layers. Plus, that smooth texture is a big giveaway.
Shale like this is often found in places like deep marine basins, lagoons, or at the
bottoms of lakes.
This rock here, which I'm pretty sure is shale, is a clastic sedimentary rock. It's got these
tiny, sand-sized particles that make it feel super smooth to the touch. You can see how it
kind of splits into these thin layers, which is a telltale sign of shale.
The way I figured out it's conglomerate is by looking at those well-rounded and well-
sorted clasts. The rounded rocks suggest they've been transported by water, and the
well-sorting means they've been sorted by size.
Conglomerate is usually found in river environments where water carries and deposits
different sediments, hence the rounded clasts from water action.
Now, this rock, I believe it's conglomerate, is also a clastic sedimentary rock, but it's a bit
different. It's made up of these clasts, which are essentially rounded or angular rocks. They
come in various sizes, from pebbles to boulders, It has a pretty coarse texture.
The way I recognized it as travertine is because of those bands. They form as minerals,
mostly calcite, and precipitate out of water as it evaporates. Travertine typically forms in terrestrial environments like caves or hot springs. It's the
result of minerals slowly precipitating from groundwater that's passed through
limestone or other mineral-rich rocks, often in cave formations or around hot spring
areas.
This last rock I believe is travertine. Which is a chemical sedimentary rock formed through
the evaporation of mineral-rich water. You can see bands or layers on the surface.