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Igneous, Sedimentary, and Metamorphic Rocks

A brief overview of the differences, similarities, and key components of the Rock Cycle.

1. What are the characteristics that make a mineral different from other solid materials on Earth?

a. The main characteristics are the mineral cannot be synthetic, cannot be made of organic molecules, and they must have atoms arranged in a rectangular repeating structure (crystal formation).

2. Describe the silicate minerals in terms of structural arrangement; in terms of composition.

a. Silicate minerals have a basic silicon-oxygen tetrahedral unit which is either isolated or joined together in the crystal structure. The structure has four unattached electrons on the oxygen atoms that can combine with metallic ions such as iron and magnesium.

3. Explain why each mineral has it’s own set of unique physical properties.

a. Each mineral has its own set of physical unique properties because it has a unique chemical composition and chemical structure.

4. Identify at least 8 physical properties that are useful in identifying minerals. From this list, identify two properties that are probably the most useful in identifying an unknown mineral. Give reasons.

a. 8 Physical properties of identifying an unknown mineral are color, streak, hardness, crystal form, cleavage, fracture, luster, and density. The most useful would be streak and crystal form. Streak because of the color of the mineral when it is finely powdered, and crystal form because the shape of a well-developed crystal form is often a great way of determining its identity.

5. Explain how the identity of an unknown mineral is determined by finding out what the mineral is not.

a. In general, the properties of a mineral is used to find out what an unknown mineral is not, so that minerals can be ruled out by certain tests.

6. What is a rock?

a. A rock is defined as an aggregation of one or more minerals and perhaps other materials that have been brought together in a cohesive solid.

7. Describe the concept of the rock cycle.

a. It essentially goes from igneous rock then weathering and erosion causes it to sediment and turn into sedimentary rock, then metamorphism occurs and it becomes a metamorphic rock, from here it can either melt from excessive heat and become an igneous rock once more or turn back into sediment.

8. Briefly explain the basic differences among the three major kinds of rocks based on the way they are formed.

a. First, I will start with igneous rocks. Igneous rocks are rocks formed from a hot, molten mass of melted rock materials (magma). Next, we have sedimentary rocks which are rocks formed from particles or previously dissolved materials from previously existing rocks (sandstone). Finally, we have metamorphic rocks which are previously existing rocks that have been changed by heat, pressure, or hot solutions into a distinctively different rock (limestone to marble).

9. Which major kind of rock, based on the way it is formed, would you expect to find most of in Earth’s crust? Explain.

a. Seeing as land is created by the heating and massive cooling of magma, I would have to say igneous rocks are the type of rocks you’d most likely see in the earth’s crust. In Hawaii, there is an active volcano that is still omitting magma into the ocean, thus creating more land.

10. What is the difference between magma and lava?

a. Magma cools slowly deep beneath the surface, whereas lava cools rapidly above the surface.

11. What is meant by the texture of an igneous rock? What does the texture of an igneous rock tell you about its history?

a. Through the texture of an igneous rock you can tell how old it is/where it came from. If it is intrusive you’ll be able to tell if it was formed under the Earth’s surface, whereas if it is extrusive you’ll be able to tell it was formed above.

12. What are the basic differences between basalt and granite, the two most common igneous rocks of earth’s crust? In what part of Earth’s crust are basalt and granite most common? Explain.

a. Granite is a course-grained igneous rock composed of light-colored, light-density, nonferromagnesian minerals. Whereas basalt is dark, high density, and is an extrusive igneous rock. You are most likely to find granite in the Earth’s continental areas, and Basalt in the ocean basins, and much of Earth’s interior.

13. Explain why a cooled and crystallized magma might have ferromagnesian silicates in the lower part and nonferromagnesian silicates in the upper part.

a. Mainly due to sediments, if it is cooled rapidly there will generally be more crystals at the top, rather than cooled slowly.

14. Is the igneous rock basalt always fine-grained? Explain.

a. Yes, because it is found generally in the ocean basins (currents are constantly pushing against it) and in Earth’s interior. Again, lots of pressure.

15. What are clastic sediments? How are they classified and named?

a. Clastic sediments are essentially weathered rock fragments. They are accumulated from rocks that are in various stages of being broken down, so there is a wide range of different sizes. The largest clastic sediments are boulders and gravel where as the smallest are silt and clay.

16. Briefly describe the rock-forming process that changes sediment into solid rock.

a. There are two steps; it goes from compaction to cementation. In compaction, the grains reduce the thickness of the sediment deposit and squeezes out any water as the grains are packed more tightly together. In the cementation process, the spaces between the sediment particles are filled with a chemical deposit.

17. What are metamorphic rocks? What limits the maximum temperatures possible in metamorphism? Explain.

a. Metamorphic rocks consist of previously existing rocks that have been changed by heat, pressure, or hot solutions into a distinctly different rock. The temperature range goes all the way up to just before magma/lava; if the rock melts it becomes an igneous rock.

18. Describe what happens to the minerals as shale is metamorphosed to slate, the schist, and the gneiss. Is it possible to metamorphose shale directly to gneiss, or must it goes through the slate and schist sequences first? Explain.

a. It is possible, it essentially just skips a ‘beat’ in the rock cycle. This is due to high temperatures, or high amounts of pressure.

19. What is the rock cycle? Why is it unique to the planet Earth?

a. The rock cycle is the process of rocks continually changing from one type to another, constantly changing from metamorphic to sedimentary to igneous. An on-going cycle.

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Comments (1)

Great, and informative Spencer!

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