Rocks and Minerals B/C

[OrigamiPlanet]

Define the following... (Click to Show Hidden Text)

1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

[dxu46]

Define the following... (Click to Show Hidden Text)

1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer (Click to Show Hidden Text)

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

[whythelongface]

Define the following... (Click to Show Hidden Text)

1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer (Click to Show Hidden Text)

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.

[OrigamiPlanet]

Define the following... (Click to Show Hidden Text)

1. Phenocryst
2. Vitreous
3. Vesicle
4. Cleavage
5. Twinning
6. Peat

Answer (Click to Show Hidden Text)

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.

[whythelongface]

New question:

Question (Click to Show Hidden Text)

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.

[orangewhale]

New question:

Question (Click to Show Hidden Text)

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 (Click to Show Hidden Text)

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.

[whythelongface]

New question:

Question (Click to Show Hidden Text)

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 (Click to Show Hidden Text)

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 (Click to Show Hidden Text)

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.

[orangewhale]

Question (Click to Show Hidden Text)

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

[dxu46]

Question (Click to Show Hidden Text)

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.... (Click to Show Hidden Text)

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)

[orangewhale]

Correct, your turn.