GEOSCI 106 Lab 2_ Rocks and minerals- Spencer March - Google Docs

GEOSCI/ENVIR ST 106: Environmental Geology Lab 2: Rocks and Minerals Assignment Overview: This assignment consists of two components: 1) a quiz on rock and mineral properties in Canvas, and 2) an application of rock identification for geological hazard assessment, which is here in this Google Doc. Submission: You will need to submit two separate items for this lab: the Canvas quiz and this Google Doc. Follow these steps: 1. Go to Canvas and complete the quiz titled “Lab 2: Rocks and Minerals (Part 1)”. 2. Return to this Google Doc and fill out each red highlighted field (_________). 3. Submit the completed Google Doc on Canvas with the following steps: a. In Google Docs, generate a PDF: File → Download as → PDF Document b. In Google Docs, use Share → Get Shareable Link, and copy the link address c. In Canvas, upload your PDF to the assignment d. Paste the link address to your Google Doc in the assignment comments. Background: Geologists often have to identify rocks and minerals based on prior experience and knowledge while out in the field in remote environments, where few tools are available. For this reason, you’ll often see geologists testing rocks’ weight, squinting at them through hand-lenses, trying to break them on different sides, or using them to scratch whatever they have around (pennies, nails, and pieces of glass are perennial favorites!). Scientifically, what geologists are trying to do is examine the density, habit, cleavage, and hardness of the minerals. Sometimes, geologists are asked to identify a rock or mineral just by looking at a picture of it. (You may find that certain friends or family members ask you to do this when they learn you’re taking a geology class.) In this lab you will answer the question: What can you learn about a rock or mineral just by looking at a picture of it? Here is a summary of the characteristics that geologists often use to identify minerals. Some of these are visual properties, which can be determined directly from photos and sometimes are enough to identify a mineral. Others of these are physical properties, which can’t be determined from photos, but which can be useful for samples that you have in hand. Visual Properties: Color : The color of the mineral in white light. Note that this is rarely definitive and can be misleading! Many minerals appear in multiple colors. For example, quartz is often colorless and translucent, but small amounts of impurities can turn it bright purple, at which point it is given another name (amethyst), even though its crystal structure still implies it is quartz. Luster : Appearance of the surface in natural light. Examples include: ● Adamantine (diamond-like brilliance) ● Resinous 1

● Greasy ● Pearly ● Silky ● Metallic ● Waxy ● Vitreous (glassy) Images with examples of these can be found here: https://en.wikipedia.org/wiki/Lustre_(mineralogy) . Habit : appearance of a single crystal or manner in which crystals grow together in aggregates. Some examples are: ● Amorphous / Massive: No crystals or grains visible ● Euhedral (Anhedral): Grains from perfect (imperfect) geometric shapes, like cubes, octagons, hexagons ● Banded: Containing distinct color bands ● Botryoidal / Globular: Forming round, ball-like shapes. ● Foliated: Crystals Like pages of a book, i.e. like overlapping sheets or leaves that often can be separated ● Granular: Many interlocking grains of approximately the same size ● Nodular / Oolitic: made up of many small rounded interlocking grains ● Radiating: thin crystals growing outward from a single point ● Specular: Reflecting, like a mirror ball ● Tabular: Crystals shaped like small tablets Physical Properties: Beyond visual appearance, the physical properties of a mineral can be further tested by examining its hardness, the patterns in which it breaks, and how it reacts to acid, magnets, and UV light. These properties are, of course, not possible to test from photos alone, but it is important to know that these are the properties that geologists rely on when visual appearance isn’t enough to definitively identify a mineral. Hardness : the resistance that a smooth surface of a mineral offers to scratching Mohs Scale Simple Test Materials 1. Talc 2. Gypsum finger nail (2.5) 3. Calcite copper penny (3.5) 4. Fluorite 5. Apatite steel knife or nail (5-6) 6. Orthoclase (a feldspar) glass (5-6) 7. Quartz Streak plate (6.5-7) 8. Topaz 9. Corundum 10. Diamond 2

Assignment Part 1. Canvas quiz. Go to Canvas and complete the quiz titled “Lab 2: Rocks and Minerals (Part 1)”. In the red highlighted box below, type “Done” when you have completed it. __Done_______ Part 2. Using rock identification to identify rockfall hazards Several million people visit Yosemite National Park each year. Most drive through Yosemite Valley under El Capitan (Figure 1), a granitic monolith that rises more than 900 meters above the valley floor. If you’ve seen the documentary Free Solo , this is the rock face that Alex Honnold aimed to climb without ropes. It’s big. Figure 1. El Capitan, Yosemite National Park. Photo from Stock and Uhrhammer (2010). 4

What many of these visitors take for granted is the ability to drive safely through the valley without getting crushed by falling rocks. Rockfall on El Capitan, however, is common. Numerous rockfall events have been captured on video in the past few years, like the relatively small event in this video: El Capitan Rockfall . Rockfall events much larger than this have happened in the past, and they will happen again in the future. The effects of rockfall are apparent at the base of the cliff, which is covered with a pile of boulders that have fallen off the cliff (see the area labeled “Rock avalanche deposit” in Figure 1), some of which are as big as the one in Figure 2. Figure 2. A boulder at the base of El Capitan that fell off the rock face about 3600 years ago. It is 11 meters across at its shortest, meaning that at least the rock broke off at least 11 meters into the cliff face when it fell. Photo from Stock and Uhrhammer (2010). An important task for the park staff is to keep visitors safe from rockfall. This requires mapping out the areas at the base of the cliffs that are at greatest risk of rockfall. This in turn requires figuring out where and when rockfall events happened in the past, including the height the rocks fell from, since that determines how fast they’re moving when they hit the ground and hence how far they travel across the valley. 5

To figure out where on the cliff these rocks came from, the authors enlisted the help of rock climbers, who took photos of the rock face during ascents of El Capitan. In Figure 4, the numbered labels show sites where some of these photos were taken. These photos contained critical clues that revealed which rock types are on which parts of the cliff. For example, their observations showed that the rock at the site #1 in Figure 4 is the Taft granite. The results are summarized in Table 1. Figure 4. Numbers show the sites where rock types were identified along climbing routes. Photo adapted from http://www.xrez.com/blog/el-capitan-gigapixel-climbing-routes/ . Table 1. Locations of rock types in Figure 4. Rock type Sites in Figure 4 with this rock type Taft granite 1, 2, 3, 11, 12, 21 El Capitan granite 6-10, 14-20, 22-24 Tonalite 4, 5, 13 (b) Your next task is to create a map of rock types on the section of El Capitan between Line A and Line B using the information in Figure 4 and Table 1. To do this, follow these steps: 1. Go to Canvas and download “El Capitan.png” from the Lab 2 module. 7

2. Return to this Google Doc and place your cursor at the red-highlighted line below these instructions, where it says “Paste your map here”. 3. In the Google Docs menu bar, click on Insert > Drawing > New. This will bring up a new window for you to create a figure in. 4. Paste the “El Capitan.png” image into this drawing space. 5. Use the Polygon tool to outline three regions, one for each rock type: the Taft granite, the El Capitan granite, and the Tonalite of the Gray Bands. A couple tips for this: a. Be sure that each rock type’s region encompasses all points (and only those points) labeled with that rock type in Table 1. b. Be sure that each polygon stays between Line A to the left and Line B to the right, and don’t extrapolate anything outside of Line A and Line B. 6. Use the Text Box tool to create a label for each rock type. To make sure the labels fit on the map easily, use short names in the labels: “Taft”, “El Capitan”, and “Tonalite”. 7. Use the Fill Color tool to create a white background for each label. This will help them show up against the background better. 8. Click Save and Close. This will paste your map into the place where the cursor was placed in Step 2. Paste your map here (5 points): ______ ____ 8