Lecture Quiz #3

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Blinn College *

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Geology

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Apr 3, 2024

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Lecture Quiz #3 Igneous Rocks 1. You are walking along and pick up a piece a granite. Give me a reasonable location for where this might be expected. Granite is a light-colored plutonic rock found throughout the continental crust, most commonly in   mountainous areas . The  Granite Mountains  are a small mountain range in San Bernardino County, California, USA, located in the Mojave Desert.  2. You are walking along and pick up a piece of basalt. Give me a reasonable location for where this might be expected. Perhaps the most famous basalt lava flow in the world is the   Giant's Causeway in Northern Ireland , in which the vertical joints form polygonal columns and give the impression of having been artificially constructed. 3. What is the geothermal gradient? Workers in underground mines know that temperatures increase as they descend deeper below Earth’s surface. Although the rate of temperature change varies considerably from place to place, it averages about 25°C (75°F) per kilometer in the upper crust. This increase in temperature with depth is known as the geothermal gradient. 4. What igneous rock was widely used for spear and arrow points? Why? Obsidian Rock was used for spear and arrow points. Because it was easy to find and work with. Obsidian is also as sharp as a surgeon’s scalpel which made it perfect to use for weapons. 5. What can you use to quickly differentiate between an extrusive and an intrusive igneous rock? Crystal size  is used to distinguish between intrusive   and extrusive igneous rocks. Intrusive rocks such as granite will have coarse crystals whereas extrusive rocks such as basalt will have fine glassy crystals. Extrusive rocks have glassy crystals as this requires rapid cooling under water. 6. Describe and define the 3 principal types of volcanoes. Shield volcano : broad, slightly dome-shaped, basaltic lava, and mild eruptions of large volumes of lava. Cinder cone volcano : built from ejected basaltic lava (mainly cinder-sized) fragments, forming a steep slope. Small size and frequently occur in groups. Composite cone volcano : also known as stratovolcano. Large, classic-shaped volcano (thousands of feet high and several miles wide at base). Composed of interbedded lava flows and layers of pyroclastic debris. Violent eruptions. Most are located adjacent to the Pacific Ocean e.g., Mount St. Helens. 7. What are the main hazards associated with volcanic eruptions? Pyroclastic flow, Lahar, Tsunamis, Volcanic ash and aviation, Volcanic gas and respiratory health, and effects on climate. 8. Why is there volcanic activity in Hawaii and Yellowstone Park? In Hawaii because it is in the middle of a plate where magma rises upward until it erupts on the seafloor, which is called a hot spot. It produces basaltic magma sources in oceanic crust. In Yellowstone Park because it is also in the middle of a hot spot. Produces granitic magma sources in continental crust. 9. What does the Snake River Plain represent?
The plain formed as the North American plate drifted southwest over a  hot spot  in Earth's crust . Today, the hot spot fuels the hundreds of geysers that give Yellowstone its fame. The thermal bulge pushed the land up, and the difference in elevation is apparent on the world map. 10. What does Devils Tower, Wyoming represent? The simplest explanation is that Devils Tower is   a stock—a small intrusive body formed by magma which cooled underground and was later exposed by erosion . In 1907, scientists Darton and O'Hara decided that Devils Tower must be an eroded remnant of a laccolith. 11. When discussion volcanic activity, what do we mean by the “Ring of Fire”? The Ring of Fire , also referred to as the Circum-Pacific Belt, is   a path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes . 12. Geologically, what is important to understand about Iceland? It is a geologically young island – less than 33 million years old – and   its majestic landscapes are shaped by active plate tectonics, volcanics, and glacial movement . It is one of the only places in the world where a divergent plate boundary is exposed at the Earth's surface! 13. Which group of minerals are the most abundant in the Earth's crust? Feldspars: The name felspar refers to a group of minerals that have alumina and silica (SiO2) in their chemical composition.  Feldspars  are the most abundant mineral group on Earth and make up nearly 60% of Earth's crust. Feldspars are used in glassmaking, ceramics, as fillers in paints, and in plastics and rubber. 14. What best defines the difference between a mineral and a rock? A mineral is a naturally occurring substance with distinctive chemical and physical properties, composition, and atomic structure. Rocks are generally made up of two of more minerals, mixed up through geological processes. 15. The process by which ions arrange themselves into orderly patterns during the cooling of a liquid is called? Crystallization is the process by which ions arrange themselves into orderly patterns during the cooling of a liquid. 16. Extrusive igneous rocks are typically finer grained than intrusive igneous rocks. Why? The extrusive magma cools quickly so the mineral grains do not have time to grow . 17. The sizes, shapes, and arrangements of mineral grains in an igneous rock are known as. Texture is the size, shapes, and arrangements of mineral grains in an igneous rock. 18. What rocks are composed almost entirely of light-colored silicates. Near one end of the continuum are rocks composed almost entirely of light- colored silicates- quartz and potassium feldspar . 19. What is composed mainly of ferromagnesian minerals. "Altramafic" means more than mafic or darker than mafic. The   altramafic rocks   consist of almost entirely ferromagnesian minerals. 20. The large mineral grains in a porphyritic igneous rock are called.
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