GEOL 121
Name: Cameron Andrew Smith
Section ___________
Rocks 1: Introduction to Rocks and Rock Processes
Scientists like to classify things - organisms, planets, stars, clouds, rocks, pretty much anything!
Classification is useful because it allows scientists to identify patterns and organize information.
In this lab, you will investigate rocks by developing your own classification scheme. You will
then learn how scientists classify rocks, and what can be interpreted about a rock’s history
based on its classification.
Learning Objectives for this Lab:
1. Identifying types of observations that are useful in identifying rocks
2. Categorize rocks based on observable physical characteristics, and explain why
classification is an important aspect of science
3. Classify rocks as sedimentary, igneous, or metamorphic, and justify why each
rock is included in its classification group
4. Reflect on how their classification schemes compared to the one used by
geologists
Part 1: Rock Exploration and Differentiation
1. In your groups, observe the samples given to you by your instructor (Sample Group A).
Below, brainstorm a list of the observable properties of the rocks that you might use to
differentiate them. The properties could be anything that you might see and note about the
rock; there is no right or wrong answer here!
●
●
●
●
Reddish color
Dark black color
Some have large crystals
Some have smaller visible crystals
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GEOL 121
2. Come up with a classification scheme for your rocks; organize your rocks into 3-6 groups. In
the table below, list the sample numbers in each group and write a description of the
characteristics that define that group. After this question, you will be working with a different
team, so all team members should record these descriptions on their own page.
Sample Numbers
1,4,6,7,10
Description
Large visible crystals
Dark colored
5,3
Reddish color
dull smooth surface
no visible crystals
2,9,12
Darker colored
Smooth, dull surface
No visible crystals
2
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GEOL 121
3. Your instructor will now assign you to new groups. In your new group, compare your
classification schemes. How are your classmates’ classification schemes similar to and different
from the one you came up with? Describe below.
They are pretty similar to the ones that we had, most of them were based on color and the
visible traits of the rocks.
4. Your instructor will give you a new set of samples (Sample Group B). Consider how effective
each of the classification schemes your group members came up with were in classifying these
samples. Then, develop and describe a revised classification scheme based on your discussion
and the introduction of the new data (samples).
A significant way to classify these works would be if they are foliated, not foliated, or no minerals
visible. This would allow for a new data set to be added easily and not base everything off of the
color and shape of the rocks.
5. Instead of rocks, imagine that your instructor had asked you to classify fruit- apples, pears,
cherries, blueberries, oranges, limes, blackberries, bananas, in order to determine how they are
related to each other.
a. Would classifying the fruit by color or size help scientists identify and distinguish
between different fruit groups? What issues could arise if these characteristics alone
were used? E.g., how would this impact the classification of new fruits (pineapple,
melons, tomatoes, avocados, etc….)
I assume that classifying a fruit by color or size would be a good starting point for
classification, but some other attributes that you could use would be if it has seeds or
not, how it grows (tree, ground, etc) if just color was and size would be used to classify
fruits there would be a huge variety of fruits that happen to be the same color, but have
very different traits.
b. Identify classification schemes that could help you divide these fruits into groups that
illustrate how they are related to each other. Are there any observable characteristics
could you use?
Some categories that I would use would be if the fruit has seeds, how it grows ex. From
a tree, ground, etc.
3
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GEOL 121
*wait for instructor guidance before beginning Part 2
Part 2: Scientific Classification of Rocks
1. Consider that geoscientists want to classify rocks in a way that illustrates how the rocks are
related to one another; in other words, which rocks are formed in similar ways?
a. Identify a classification scheme that could help you divide the rocks into groups that
illustrate how they are related to each other.
How the rocks formed. Igneous, metamorphic and sedimentary rocks.
b. Are there any of the observable characteristics you saw that could help you divide the
rocks into groups based on this classification scheme? Consider the following:
i.
Would rock color help scientists determine how rocks are related to each other?
Justify your answer.
Yes, the color would help scientists identify the composition of the rocks and what
they are made up of.
ii.
Would rock texture be able to help scientists determine how rocks are related to
each other? Justify your answer.
Yes, the texture of the rocks would greatly help identify the rocks. If there are
visible crystals, or a smooth surface on the rock it would help identify what the
rock is made up of or how it formed. For example, Sandstone has a very sandy
texture.
iii.
What characteristics other than color and texture might scientists look at in
determining rock classification? Why?
The location that the rocks were found or collected could tell the scientist how the
rocks were actually formed and the age of the rock.
4
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GEOL 121
At this point, your instructor will lead you in a discussion of the accepted scientific
classifications for the three primary rock types, and subcategories within each. As part
of this discussion, fill out the “identifying characteristics” column of the table on the next
page.
2.Fill out the “identifying characteristics” column based on information provided by your instructor.
ROCK TYPE
Igneous
SUB-TYPE
FORMATION
MECHANISM
Forms from the cooling
and crystallization of
Extrusive
molten rock on the
Earth's surface.
IDENTIFYING CHARACTERISTICS EXAMPLES
Have very small crystals that
cannot be seen without a
microscope. Interlocked
crystals.
Forms from the cooling
and crystallization of Have large crystals that can be
Intrusive
seen with the human eye. Not
molten rock underneath
interlocked crystals.
the Earth's surface.
Detrital
Forms from the
accumulation and
cementation of small
particles (sediments)
on/near the Earth's
surface.
Chemical
Forms from the
precipitation of
materials from water
on/near the Earth's
surface.
Sedimentary
Metamorphic
Basalt
Granite
No fossils, has clasts, sandy
Sandstone
texture
Has fossils, no clasts and
reacts to HCL
Forms when rocks are
subjected to some
The minerals are arranged in
Foliated
combination of high
lines
heat, high pressure, and
hot mineral-rich fluids.
Limestone
Gneiss
5
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GEOL 121
Forms when rocks are
subjected to some
The minerals are scattered
Nonthroughout the rocks with no
combination of high
Foliated
pattern.
heat, high pressure, and
hot mineral-rich fluids.
Marble
3. Fill out the first three columns of the chart below, classifying each sample from Sample
Group A according to the sub-type described on the previous page. Include a description of your
reasoning; what observations support your hypothesis?
Rock
Sample #
Hypothesized
Classification &
Formation
Mechanism
Supporting Observations
& Reasoning
Corrected
Classification
& Formation
Mechanism
Supporting
Observations &
Reasoning
3
Igneous
Extrusive
Small Crystals
Igneous
Intrusive
Large interlocking
crystals, more than one
mineral present,
minerals randomly
oriented
5
Detrital
Sedimentary
Sandy Smooth Surface
Sedimentary
Detrital
Small clasts
10
Intrusive
Igneous
Large Visible Crystals
Igneous
extrusive
Small interlocking
crystals, more than one
mineral present
1
The Problems of
Identity
(examples)
Minerals are randomly
spread out throughout the
rock.
Metamorphic
, foliated
Interlocking crystals
aligned in layers
2
Sedimentary
Chemical
Smooth texture, no clasts
Metamorphic
, non foliated
Interlocking crystals of
one mineral
4
Non-Foliated
Metamorphic
Dispersed minerals
throughout the rock no
pattern
Sedimentary,
detrital
Small clasts
7
Non-Foliated
Metamorphic
There are dispersed
minerals throughout the
rock
Igneous
intrusive
Large interlocking
crystals, more than one
mineral present,
minerals randomly
orientated
9
Chemical
Sedimentary
Smooth texture, but not
sandy
Sedimentary,
chemical
Fizzes with HCL mineral
present
6
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GEOL 121
12
Detrital
Sedimentary
Smooth Sandy Texture
Igneous
extrusive
Small interlocking
crystals, more than one
mineral present
Check your answers from question 2 with your instructor before moving on in the lab. Fill out
the last two columns on the table based on instructor feedback.
4. Repeat this process with Sample Group B.
Rock Sample #
Hypothesized
Classification & Formation
Mechanism
Supporting Observations & Reasoning
4
Intrusive Igneous
Very small crystals that can't really be
seen without a microscope. Shiny
13
Foliated Metamorphic
The minerals are formed in lines.
17
Non-foliated Metamorphic
There are minerals spread throughout
the rock
14
Detrital Sedimentary
Sandy texture with smaller clasts
15
Chemical Sedimentary
This rock reacts to HCL, and doesn’t
have any clasts
16
Igneous Extrusive
Has very small crystals that can’t really
be seen without a microscope, but is
shiny.
7
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GEOL 121
Part 3: Reflection
1. Reflect on the ease of implementation of the classifications your groups developed in Part 1
of the lab, versus the geologist-defined classifications.
a. Which system of classification is easiest to use? Why?
In my opinion, I think that the systems that scientists have developed are much easier to
use than the ones that my group came up with in class. They use very precise structures
and features to describe these rocks, while we grouped them by color and shape.
b. Which system of classification is the most useful? Justify your answer, including a
discussion of what you are defining as “useful”
The Metamorphic, Sedimentary, Igneous system of organization is the most useful
because it makes it easy to look at any given rock and be able to tell what group it falls
under. I would define useful as something that it easy to use, but also gives good
information and insight into how the rocks formed and their specific structure
c. Explain why classification systems are common across all branches of science, and how
scientists may decide what types of observations would be useful to use in classifying
rocks, objects, organisms, etc.
Classification systems are very common across all branches of science because they
are a very useful tool to organize and describe many different things from rocks to
organisms.
2. Imagine you’re on a trip with a friend and they do not have a background in geology. You
both see a rock outcrop and your friend wonders what type of rock the outcrop is made of.
a. In a few sentences, how would you describe to your friend what to look for to determine
the rock type?
I would tell my friend to first look for visible crystals then the organization of the minerals
in the rock.
8
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GEOL 121
b. Give a brief description (a few words) of what observations you would expect your friend
to make if the rock is:
i.
Igneous intrusive: Large visible crystals
ii.
Igneous extrusive: Small crystals that are not really visible by the human eye, but
might appear slightly shiny.
iii.
Foliated metamorphic: Minerals that are grouped in lines
iv.
Non-foliated metamorphic: Lots of different colors and minerals, but they are
spread out throughout the rock and not very organized.
v.
Detrital sedimentary: Has small chunks of rocks, doesn’t have any fossils
vi.
Chemical sedimentary: Could have fossils, but shouldn’t have any chunks of rock
sticking out.
3. What aspects of making observations, rock classification, and/or the six rock categories
defined in this lab do you feel most confident about?
I feel that I know the different traits of the 6 rock classifications.
4. What aspects of making observations, rock classification, and/or the six rock categories
defined in this lab do you still have questions about?
I just need to practice by looking at actual rocks and identifying the characteristics that I see
and then matching it with a classification of rock. I have no questions though this is very
interesting!
9
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