1 separate the intrusive coarse grained rocks in the

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1. Separate the intrusive (coarse-grained) rocks in the Activity 2 tray from the extrusive (fine-grained or porphyritic) rocks. Texture Interpretation Fine-grained: few or no visible crystals (<2mm) Porphyritic: mix of coarse and fine grained textures Fast cooling at or near surface of the Earth Two cooling stages Coarse-grained: visible crystals (>2mm) Slow cooling at great depths 2. Arrange the fine-grained/porphyritic and coarse-grained piles in order from light-colored to dark-colored as shown below. Your ability to judge can be improved by looking at the minerals in the coarse-grained samples as you did in Activity 1. This ordering approximates the chemical composition of the samples. Compositions Felsic Intermediate Mafic Ultramafic Fine-grained Light-Colored Intermediate Color Dark-Colored (no common equivalent) Coarse-grained Light-Colored Intermediate Color Dark-Colored Dark or Green 3. Once you’ve arranged the rocks, ask your TA to come check your work. Now record the sample # and rock name in the appropriate space in the chart on the next page. Use Fig. 8 to help you identify the rocks. Be sure to include rock texture descriptions if the rocks are porphyritic or vesicular. Color Light Medium Dark Dark/Green Composition Felsic Intermediate Mafic Ultramafic Texture: Fine-grained (extrusive/ volcanic) Sample #: ________ Name:___________ Sample #: ________ Name:___________ Sample #: ________ Name:___________ RARE (no sample) Texture: Coarse-grained (intrusive/ plutonic) Sample #: ________ Name:___________ Sample #: ________ Name:___________ Sample #: ________ Name:___________ Sample #: ________ Name:___________ TA CHECK ____________
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Lab #2: Igneous Rocks 41 Activity 3: Understanding Density and Plate Tectonics Much of the reason plate tectonics works is because of density differences between major sections of the planet. In this activity, you first identify some additional igneous rock samples, and then measure their physical properties (mass and volume). With these data you can then calculate their densities. Follow the steps below. 1. After looking at the rock samples for this activity, identify each rock and write the name in the second column of the chart below. 2. Using the scale, weigh each rock sample and write down your measurement in the table. Always include units . 3. To measure the volume of the sample we will measure the volume of water that is displaced when the rock is submerged. Step 1 : the graduated cylinder should be about half full of water. Before you submerge the rock, very carefully and accurately measure the top of the water. Always note the value of a tick mark . Step 2 : gently submerge the rock in the cylinder, trying hard not to get your hands (or anything else) wet we want to keep all the water in the cylinder. Step 3 : very carefully and accurately measure the new height of the water. Step 4: calculate the change in volume of the water and record your answer in the table.
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