Rocks and Minerals B/C

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Re: Rocks and Minerals B/C

Postby ScottMaurer19 » September 28th, 2017, 3:28 pm

whythelongface wrote:
dxu46 wrote:
whythelongface wrote:
That appears to be right to me. I think you can just ask the next question if you'd like.

Question
Image
1. What is the rock?
2. What is the mineral?
3. Name the area where the rock is most commonly found.
4. What is the rock's plutonic equivalent.


Answer
1. Looks like a really bubbly basalt, even edging into scoria
2. Olivine
3. Basalt is a very prevalent rock in oceanic crust and mafic lava flows. Scoria is found as bombs and tephra from volcanic eruptions.
4. Gabbro

Probably vesicular basalt
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Re: Rocks and Minerals B/C

Postby dxu46 » September 28th, 2017, 3:47 pm

ScottMaurer19 wrote:
whythelongface wrote:
dxu46 wrote:
Question
Image
1. What is the rock?
2. What is the mineral?
3. Name the area where the rock is most commonly found.
4. What is the rock's plutonic equivalent.


Answer
1. Looks like a really bubbly basalt, even edging into scoria
2. Olivine
3. Basalt is a very prevalent rock in oceanic crust and mafic lava flows. Scoria is found as bombs and tephra from volcanic eruptions.
4. Gabbro

Probably vesicular basalt

It's vesicular basalt. whythelongface, your turn!

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Re: Rocks and Minerals B/C

Postby whythelongface » September 28th, 2017, 7:16 pm

Question
Image
1. What is the unlabeled region in this triangular plot known as?
2. What is the difference between orthoclase and monocline?
3. Under a polarized thin section, what is the easiest way of differentiating plagioclase, monocline, orthoclase, and quartz?
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Re: Rocks and Minerals B/C

Postby OrigamiPlanet » September 29th, 2017, 12:46 pm

whythelongface wrote:
Question
Image
1. What is the unlabeled region in this triangular plot known as?
2. What is the difference between orthoclase and monocline?
3. Under a polarized thin section, what is the easiest way of differentiating plagioclase, monocline, orthoclase, and quartz?

Answer
1. High temperature compositional region?
2. Orthoclase lacks lamellar twinning whilst microcline does, and microcline is the only one that can be in a darker color/blue-green.
3. Look for cleavage: If it lacks cleavage than it is likely quartz. I'm not sure with plagioclase, monocline and orthoclase other than the color composition.
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Re: Rocks and Minerals B/C

Postby whythelongface » September 29th, 2017, 2:04 pm

OrigamiPlanet wrote:
whythelongface wrote:
Question
Image
1. What is the unlabeled region in this triangular plot known as?
2. What is the difference between orthoclase and monocline?
3. Under a polarized thin section, what is the easiest way of differentiating plagioclase, monocline, orthoclase, and quartz?

Answer
1. High temperature compositional region?
2. Orthoclase lacks lamellar twinning whilst microcline does, and microcline is the only one that can be in a darker color/blue-green.
3. Look for cleavage: If it lacks cleavage than it is likely quartz. I'm not sure with plagioclase, monocline and orthoclase other than the color composition.


Not really
Admittedly this was a bit harder than usual.
1. The answer I was looking for was "Miscibility gap". This is a region on the triangular plot where no solid form of the chemical composition described there exists. In other words, there is a gap in mixing of different endmember elements.
2. Yes, but I was thinking of something more general, as in formation. Microcline is formed from the slow cooling of alkali feldspar species. It is also triclinic as opposed to microcline, which is monoclinic.
3. Under a cross-polarized microscope, one can readily see vertical lines in plagioclase minerals - that's because it twins following the albite law. Orthoclase crystals have more horizontal cleavage, which is also easily spotted. Microcline will usually have a grid-iron pattern of scratches on crystal surfaces. Quartz is more uniform, has a weaker and often undulatory birefringence pattern. What this means is that the extinction of cross-polarized light is not very apparent when you rotate the crystal.


Your turn.
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Re: Rocks and Minerals B/C

Postby OrigamiPlanet » October 3rd, 2017, 12:40 pm

Define the following...
1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat
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Re: Rocks and Minerals B/C

Postby dxu46 » October 3rd, 2017, 2:24 pm

OrigamiPlanet wrote:
Define the following...
1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer
1. a crystal on a rock that is especially conspicuous
2. glassy or looking like glass
3. air pockets
4. a sharp division
5. two or more crystals forming within each other.
6. the lowest grade of coal, with lowest carbon concentration

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Re: Rocks and Minerals B/C

Postby whythelongface » October 3rd, 2017, 9:12 pm

dxu46 wrote:
OrigamiPlanet wrote:
Define the following...
1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer
1. a crystal on a rock that is especially conspicuous
2. glassy or looking like glass
3. air pockets
4. a sharp division
5. two or more crystals forming within each other.
6. the lowest grade of coal, with lowest carbon concentration


I'd make the following corrections:
4. Cleavage is the way the atoms in a crystal split along weaker surfaces.
5. Multiple crystals in different orientations, sharing a common surface
6. Peat is the precursor of coal, it is organic matter that has not yet been metamorphosed.
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Re: Rocks and Minerals B/C

Postby OrigamiPlanet » October 4th, 2017, 12:48 pm

whythelongface wrote:
dxu46 wrote:
OrigamiPlanet wrote:
Define the following...
1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer
1. a crystal on a rock that is especially conspicuous
2. glassy or looking like glass
3. air pockets
4. a sharp division
5. two or more crystals forming within each other.
6. the lowest grade of coal, with lowest carbon concentration


I'd make the following corrections:
4. Cleavage is the way the atoms in a crystal split along weaker surfaces.
5. Multiple crystals in different orientations, sharing a common surface
6. Peat is the precursor of coal, it is organic matter that has not yet been metamorphosed.

dxu46, you are still right to an extent, but I would prefer whythelongface's response with the last three as they are more accurate.
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Re: Rocks and Minerals B/C

Postby whythelongface » October 7th, 2017, 6:01 pm

New question:
Question
1. What is the defining characteristic of sedimentary rocks in a low-energy environment of formation?
2. What is SEDEX?
3. From what mineral does Kaolinite form from?
4. What is a metamorphic facies? Give an example.
5. Explain fractional crystallization.
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He went out and hanged himself and then there were none."

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Re: Rocks and Minerals B/C

Postby orangewhale » October 13th, 2017, 11:05 am

whythelongface wrote:New question:
Question
1. What is the defining characteristic of sedimentary rocks in a low-energy environment of formation?
2. What is SEDEX?
3. From what mineral does Kaolinite form from?
4. What is a metamorphic facies? Give an example.
5. Explain fractional crystallization.


Answer
1. Angular fragments
2. Sedimentary exhalative deposits
3. Feldspar (not sure which type of feldspar)
4. Distinct mineral assemblages resulting from different formation environments. Example: greenschist facies result from low grade metamorphism
5. Since minerals crystallize at different temperatures, certain minerals will crystallize as a melt cools and separate from the melt. It's one way that magmatic differentiation takes place.

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Re: Rocks and Minerals B/C

Postby whythelongface » October 13th, 2017, 7:14 pm

orangewhale wrote:
whythelongface wrote:New question:
Question
1. What is the defining characteristic of sedimentary rocks in a low-energy environment of formation?
2. What is SEDEX?
3. From what mineral does Kaolinite form from?
4. What is a metamorphic facies? Give an example.
5. Explain fractional crystallization.


Answer
1. Angular fragments
2. Sedimentary exhalative deposits
3. Feldspar (not sure which type of feldspar)
4. Distinct mineral assemblages resulting from different formation environments. Example: greenschist facies result from low grade metamorphism
5. Since minerals crystallize at different temperatures, certain minerals will crystallize as a melt cools and separate from the melt. It's one way that magmatic differentiation takes place.


Basically all correct
Except 1; The answer to that one was "small sediment size". Think about it this way: in a high-energy EoF, such as a stream bed, fine sediments would be washed out of the system. An example of a low-energy EoF would be the bottom of a very still lake, where silt could accumulate.


Your turn.
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"One little Sciolyer left all alone,
He went out and hanged himself and then there were none."

Congratulations to WW-P South for winning 14th place at Nationals!

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Re: Rocks and Minerals B/C

Postby orangewhale » October 17th, 2017, 10:31 am

Question
1. Describe idiochromatic, allochromatic, and pseudochromatic, and give an example of each.
2. What is the difference between a phenocryst and a porphyroblast?

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Re: Rocks and Minerals B/C

Postby dxu46 » November 9th, 2017, 5:11 pm

orangewhale wrote:
Question
1. Describe idiochromatic, allochromatic, and pseudochromatic, and give an example of each.
2. What is the difference between a phenocryst and a porphyroblast?

Funny, we just had a test at our R&M meeting about both topics....
1. Idiochromatic - in which a mineral is colored due to its natural properties (e.g. malachite)
Allochromatic - in which a mineral is accidentally colored due to impurities (e.g. quartz)
Pseudochromatic - in which a mineral undergoes a color change because of optical and/or physical properties (e.g. tarnished bornite)
2. Rock type (phenocryst is in igneous, porphyroblast is metamorphic)

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Re: Rocks and Minerals B/C

Postby orangewhale » December 1st, 2017, 2:52 pm

Correct, your turn.


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