lab igneous
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Geology
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Dec 6, 2023
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GEOL 1100 500
Igneous Rocks
Pre-Lab, Lab Report and Applications
Pre-Lab
Answer the following questions after reading the text and watching the assigned videos (Canvas), or any other source that you find helpful. See vocabulary list in the instructions.
Textures of Igneous Rocks
1.
What term
is used to describe the size and arrangement of the crystals in an igneous rock? APHANITIC TEXTURE
2.
What process
has the greatest effect on this term? Rapid cooling
3.
What can be said of the texture
of an igneous rock that cools at the surface of Earth? ____
very fine-grained or even glassy ___________________
4.
Give an example of the name of a rock
with this description of texture? obsidian
5.
What rock is the result of a non-orderly (amorphous) structure?
amber
6.
What igneous rock floats in water?
pumice
7.
What is the name of the texture
for this rock? Vesicular
8.
What are the three most common categories of texture
for crystalline igneous rocks?
___
Phaneritic________________ _______
Porphyritic_____________ ________
Pyroclastic.___________
9.
What other textural classifications
are there?
10.
_____
Diorite______________ ____
Felsic________________
______
Andesite_____________
Minerals in Igneous Rocks
11.Name the 8 minerals commonly found in igneous rocks. Spelling counts.
K-feldspar, quartz, plagioclase, pyroxene, olivine, muscovite, biotite, and amphibole
12.A rock consisting of the three lightest-colored minerals (from the list above), with a phaneritic texture, would be classified as a _____felsic________________.
13.
Light colored igneous rocks are rich in quartz
and feldspar.
(mineral names).
14.
Dark colored igneous rocks have large amounts of iron___________
and ____magnesium____ (element names). 15.Name the phaneritic rock type that consists of 50% light and 50% dark minerals:
___granite________________ What is its aphanitic equivalent? Rhyolite 16. Match the following rock name to their texture and composition by placing their names in the spaces below: gabbro, diorite, rhyolite, andesite, granite, basalt
Mafic
Intermediate
Felsic
Aphanitic
gabro
diorite
granite
Phaneritic
basalt
andesite
rhyolite
Lab Exercise
Use the lab instructions for details, especially for the reflection. A.
Igneous Minerals
Write the name for the eight minerals common to igneous rocks (from 11 above), and at
least two diagnostic
properties. One has been done as an example. Quartz:
hard, vitreous, translucent, conchoidal fracture
K-feldspar: pegmatites, low temperature hydrothermal veins
Plagioclase: primary aluminium-bearing
mineral in mafic rocks formed at low pressure.
Muscovite: abundant silicate mineral that contains potassium and aluminum.
Biotite: a silicate mineral in the common mica group
Amphibole:
refers not to a single mineral, but to a group of minerals.
Pyroxene: common in meteorites and in extrusive igneous rocks, especially basalt
Olivine: magnesium iron silicate with the chemical formula
B.
Igneous Rock Descriptions and Identification
Fill in each line. If not applicable, enter N/A. Please use a different color or font to distinguish your answers. (Note: if your samples are labeled differently, change the labels). Rock A
NAME: Basalt
1.
Color:
dark-colored
2.
Composition (mafic/felsic): mafic
3.
Texture: fine-grained
4.
Visible minerals (if any): plagioclase and pyroxene
5.
Intrusive/extrusive: extrusive
6.
Environment of formation: form in small intrusive bodies, such as an igneous dike or
a thin sill. 7.
Bowen’s Reaction Series: 8.
Other observations:
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Rock B
NAME: pumice
1.
Color:
2.
Composition (mafic/felsic):
3.
Texture:
4.
Visible minerals (if any):
5.
Intrusive/extrusive:
6.
Environment of formation: 7.
Bowen’s Reaction Series: 8.
Other observations: Rock C
NAME: obsidian
1.
Color: dark
2.
Composition (mafic/felsic): felsic
3.
Texture: smooth uniform texture
4.
Visible minerals (if any): mineraloid
5.
Intrusive/extrusive: extrusive
6.
Environment of formation: along the edges of a lava flow
7.
Bowen’s Reaction Series: 8.
Other observations:
Rock D
NAME: rhyolite
1.
Color: pink or gray
2.
Composition (mafic/felsic):felsic
3.
Texture: small grains
4.
Visible minerals (if any): hornblende and biotite. 5.
Intrusive/extrusive: extrusive
6.
Environment of formation: magmas erupt
7.
Bowen’s Reaction Series: 8.
Other observations: Rock E
NAME: dacite
1.
Color: light
2.
Composition (mafic/felsic): felsic
3.
Texture: grainy 4.
Visible minerals (if any): rhyolite and andesite 5.
Intrusive/extrusive: extrusive
6.
Environment of formation: in subduction zones were a relatively young oceanic plate
is subducting under a continental plate. 7.
Bowen’s Reaction Series:
8.
Other observations: Rock F
NAME: scoria
1.
Color:
dark-colored
2.
Composition (mafic/felsic): mafic
3.
Texture: bubble-like cavities
4.
Visible minerals (if any):
5.
Intrusive/extrusive: extrusive
6.
Environment of formation: magma containing abundant dissolved gas flows from a volcano or is blown out during an eruption.
7.
Bowen’s Reaction Series: 8.
Other observations: C.
Application Questions: (refer to Chapter 4 and handouts for help).
1. Igneous rocks form by:
when hot, molten rock crystallizes and solidifies
2. Why does magma move to the surface? Magma rises through the Earth's crust because it is less thick and more buoyant than the nearby rock.
3. a. What are extrusive
igneous rocks?
When magma escapes and cools
above (or very near) the Earth's surface, extrusive, or volcanic, igneous rock is created.
b. What are intrusive
igneous rocks?
When magma is imprisoned deep
within the Earth, intrusive, or plutonic, igneous rock is created.
4. Match the following geologic terms with their definitions:
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a pluton
a. a collection plutonic bodies d volcano
b. a vertical intrusion of igneous material
e dike
c. magma that chills before reaching the surface
b sill
d. the surface expression of magma eruption
c batholith
e. an igneous intrusion that follows original bedding planes and is usually horizontal
17. Granitic rocks are normally found on the active plate boundaries
while basaltic rocks make up most of the ocean
floor
.
18. Most of Yosemite National Park is composed of a granodiorite batholith. Are these rocks intrusive or extrusive? _____intrusive__________________
19. Yellowstone National Park in Wyoming overlies a hot spot beneath the continental crust. What types of features (general term) would you find in this park, that are related to the igneous activity?
(Hint: Think about what makes Yellowstone famous).
Yellow stone has more geysers and hot springs than any other place on earth, and it lies atop a dormant volcano.
D. Lab Reflection: Instructor’s Grading Rubric:
Superior
Developing
Lacking
Pre-lab
Mostly correct answers. Some errors or omissions, and/or indication that instructions were not followed.
Incomplete and/or there are multiple errors.
8-10 points
6-8 points
0-5
Rock Descriptions and Identification
All 10 identification sections are complete and logical, with
minimal errors; answers are recorded for all 6 diagnostics, the “other features” when appropriate, and a rock name is recorded
10-15 points
Some errors or omissions, and/or indication that instructions were not followed.
5-10 points
Incomplete and/or there are multiple errors.
0-5 points
Applications
Questions
Mostly correct answers. 8-10 points
Some errors or omissions, and/or indication that instructions were not followed.
6-8 points
Incomplete and/or there are multiple errors.
0-5
Reflection
Thoughtful reflection on any problems encountered, interesting discoveries, etc.
15 points
Reflection is lacking in detail.
5-9 points
Minimal or no reflection.
0-4 points
TOTAL: /50