Igneous Rock lab without kit final
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School
Lone Star College System, North Harris *
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Course
1401
Subject
Geology
Date
Apr 3, 2024
Type
docx
Pages
2
Uploaded by CoachFinchMaster481
Directions
: Complete the following questions using three (3) reputable
online sources (not Wikipedia). All answers must at least two (2) complete sentences in length. Your responses must be in your own words. You will NOT
be awarded credit for copying and pasting directly from online sources.
•
How do igneous rocks form?
Igneous rocks form through the cooling and solidification of molten magma or lava. This process can occur either beneath the Earth's surface, leading to intrusive igneous rocks, or on the surface, resulting in extrusive igneous rocks.
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What is the difference between magma and lava?
Magma is molten rock beneath the Earth's surface, while lava is molten rock that reaches the Earth's surface. Once magma erupts, it becomes lava.
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Describe the difference between aphanitic and phaneritic texture.
Aphanitic texture refers to fine-grained igneous rocks with crystals too small to be seen with the naked eye, often resulting from rapid cooling. Phaneritic texture, on the other hand, describes coarse-grained rocks with visible crystals, typically formed through slow cooling deep within the Earth.
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Describe the difference between a mafic and a felsic rock.
Mafic rocks, such as basalt, are rich in dark minerals like iron and magnesium, resulting in a darker color and higher density. Felsic rocks, like granite, are dominated by light-colored minerals like quartz and feldspar, leading to a lighter color and lower density.
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Define porphyritic texture.
Porphyritic texture is characterized by the presence of large crystals, known as phenocrysts, embedded in a fine-grained matrix or groundmass. This texture indicates a two-stage cooling process, where the larger crystals form during slower cooling beneath the Earth's surface, followed by rapid cooling for the surrounding matrix at or near the surface.
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What are vesicles and how do they form?
Vesicles are small cavities or voids in volcanic rocks that result from the presence of gas bubbles, usually steam or other volatiles, trapped during the rapid cooling and solidification of lava. As lava erupts and reaches the Earth's surface, the pressure decreases, causing the previously dissolved gases to form bubbles, creating vesicles in the solidified rock.
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What are phenocrysts? Phenocrysts are large, well-formed crystals found in porphyritic igneous rocks, distinctly larger than the surrounding groundmass crystals. They typically represent minerals that crystallized earlier during the slower cooling phase beneath the Earth's surface before the rapid cooling that formed the finer-grained matrix.
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Site your sources:
“What Is the Difference between Magma and Lava.” Earth Observatory of Singapore
, earthobservatory.sg/earth-science-education/earth-science-faqs/volcanoes/what-is-the-
difference-between-magma-and-lava. Accessed 29 Feb. 2024. Website for Queensborough Community College
, www.qcc.cuny.edu/biologicalSciences/faculty/RScal/Physical%20Geology/
chap3.html#:~:text=APHANITIC%20TEXTURE%20%2D%20Igneous%20rocks
%20that,in%20an%20underground%20magma%20chamber. Accessed 29 Feb. 2024. “Vesicles: What Are They? Types, Structure, and Function.” Medical News Today
, MediLexicon International, www.medicalnewstoday.com/articles/vesicle. Accessed 29 Feb. 2024. •
Using Google Draw, or a similar drawing program, sketch an image of an igneous rock that clearly illustrates porphyritic texture
. You may insert your drawing at the end of this document or attach it separately to the assignment dropbox. Do the best that you can here!
•
Using Google Draw, or a similar drawing program, sketch an image of an igneous rock that clearly illustrates aphanitic texture containing phenocryts
. You may insert your drawing at the end of this document or attach it separately to the assignment dropbox. Do the best that you can here!
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