Rocks Lab 1 - Tim Trostel

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Colorado State University, Fort Collins *

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121

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Geology

Date

Dec 6, 2023

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docx

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GEOL 121 Tim Trostel Section L18 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! ● Color ● Size ● Luster

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. Sample Numbers Description 2, 4, 7, 8, 9, 10 All of these rocks are dark in color. 1, 3, 10, 11 All of these rocks contain obvious crystals inside of them. 5, 6, 12 All of these rocks are lighter in color. 3. Discuss your classification scheme with another table group. How are your classmates’ classification schemes similar to and different from the one you came up with? Describe below. 2

GEOL 121 The other group did smooth, shiny, matte, unsmooth, dark and light. We did have a few of the same classifications but they had a few more groups to divide their rocks into. 4. Your instructor will give you a new set of samples (Sample Group B). Consider how effective each of the classification schemes your group and your neighbor group \ 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). Our last scheme was fairly effective but we could have come up with a couple more ideas to classify them even better. ● Color ● Luster ● Matte ● Rough ● Smooth ● Hardness 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….) The scientists should classify the fruits by color as that will narrow down each group to only one or two fruits per group. Though if only color was used to classify the fruits a big issue would arise. This issue is that many fruits are the same color. More than just one characteristic must be used to classify the fruits. With new fruits the same problem would occur as it introduces many more fruits that have the same color as each other and some of the existing fruits. 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? I would classify the fruits based on what types of seeds they have, interior or exterior. This is an observable characteristic. 3

GEOL 121 *wait for instructor guidance before beginning Part 2 Part 2: Scientific Classification of Rocks 1) 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, which is based on how the rocks form. As part of this discussion, fill out the “identifying characteristics” column of the table below. ROCK TYPE SUB-TYPE FORMATION MECHANISM IDENTIFYING CHARACTERISTICS EXAMPLES Igneous Extrusive Forms from the cooling and crystallization of molten rock on the Earth's surface. Extrusive igneous rocks do not have visible crystals very often as they cool quickly and are fine grain. They sometimes have a perforated look to them from bubbles being trapped when they cool. Basalt Intrusive Forms from the cooling and crystallization of molten rock underneath the Earth's surface. Intrusive igneous rocks have large visible crystals because they cool slower under the surface of the earth. Granite Sedimentary Detrital Forms from the accumulation and cementation of small particles (sediments) on/near the Earth's surface. Detrital rocks are clastic meaning that they are made from compaction and cementation. If the grain size is large you can see some of the rocks that make it up. Sandstone Chemical Forms from the precipitation of materials from water on/near the Earth's surface. Chemical rocks are formed from silt and dissolved ions from evaporation. It can be classified by the types of minerals that make it up. Limestone Metamorphic Foliated Forms when rocks are subjected to some combination of high heat, high pressure, and hot mineral-rich fluids. Foliated rocks have visible layers from all the different rocks and minerals being squeezed on top of one another during high heat and pressure. Gneiss 4

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