Volcanic Andesite Rock Identified
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10 ماه پیش
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This video features the igneous
This video features the igneous rock called andesite (using 360 degree photography). Note that this rock sample is an andesite porphyry, containing many very small white spots of the mineral plagioclase. Andesite is an extrusive, intermediate, fine-grain rock that usually is a medium-gray color. Andesite porphyry is a sort of gritty lava, with both visible solid and microscopic components (that were liquid before cooling) in the lava flow. It is sort of like a volcanic soup with white diced onions (of plagioclase minerals) in a broth--like French onion soup.
Sometimes, cooled lava will form vertical joints (or cracks) from the original ground surface and to the lava surface. In crystalized lavas, joints can form as the cracks extend into the cooling lava as it cools.
Note that there is a range or gray colors associated with intermediate igneous rocks. So, it may take time to learn where the color threshold is between darker-gray (intermediate rock) and dark (mafic rock) colors. Similarly, you will need to learn where the color threshold is between lighter-gray (intermediate rock) and light (felsic rock) colors. Be aware that intermediate rocks contain intermediate amounts of iron and magnesium too. Therefore, andesite can rust a little, but generally is not as deeply rusted as a mafic rock (such as a basalt), or an ultramafic rock (such as a dunite). Usually intermediate rocks weather to a slightly brown, tan, or yellowish-brown color. Note again that mafic rocks and ultramafic rocks weather much more significantly than intermediate rocks. Mafic rocks usually weather into dark-brown, reddish-brown, or orangish-brown colors--and dunite usually weathers into a yellowish-brown or brown color.
Hello Rock People! This is Dave the Geology Dude! Identification notes for this rock are below in this text. Please be aware that the only way to really learn rock identification, is to have hands-on experience. This is because visual experiences alone do not show properties like hardness, acid reactivity, density, and the range of variables that are common to each rock type. Don't forget that Geology isn't rocket science--it's Rock Science! Please "like" and subscribe to this YouTube channel!
Identification information for this rock:
1) color: andesite usually has a range of medium-gray colors. Note that andesite can be either slightly darker, or slightly lighter, than medium-gray.
2) grain size: porphyry--which is both coarse and fine grain size
3) hardness: generally about as hard glass (for unweathered, clean samples). Note that hardness tests usually are oriented to pure minerals--and not to rocks. This is because rocks usually contain a variety of different minerals (that individually may create different localized areas with different hardnesses within the rock). So, hardness tests usually are not performed on rocks that contain a mix of minerals.
4) composition: andesite is intermediate. So it contains a microscopic combination of plagioclase, hornblende, and biotite.
5) acid reactivity: does not react to acid
6) classification: it is an extrusive, intermediate igneous rock (volcanic)
7) density: it is about as dense other igneous rocks. Note that some types of andesite may contain areas with many vesicules or bubbles--which may affect density. But if an intermediate rock contains almost all vesicles, (which causes a much lower density rock than normal)--then that rock is probably a pumice--and not an andesite. Note that pumice can be either intermediate or felsic in composition.
8) environmental association: typically is found along subduction zone volcanic areas
9) summary: if a rock is medium-gray in color, and does not react to acid contact, or contain fossils, or contain layers--then it is probably an andesite. Again, the rock may have to be broken to observe the interior color and minerals.
Music (Youtube Audio Library): Get Tough (by TrackTribe)
Copyright by David Knoblach, 2023. All rights reserved
Sometimes, cooled lava will form vertical joints (or cracks) from the original ground surface and to the lava surface. In crystalized lavas, joints can form as the cracks extend into the cooling lava as it cools.
Note that there is a range or gray colors associated with intermediate igneous rocks. So, it may take time to learn where the color threshold is between darker-gray (intermediate rock) and dark (mafic rock) colors. Similarly, you will need to learn where the color threshold is between lighter-gray (intermediate rock) and light (felsic rock) colors. Be aware that intermediate rocks contain intermediate amounts of iron and magnesium too. Therefore, andesite can rust a little, but generally is not as deeply rusted as a mafic rock (such as a basalt), or an ultramafic rock (such as a dunite). Usually intermediate rocks weather to a slightly brown, tan, or yellowish-brown color. Note again that mafic rocks and ultramafic rocks weather much more significantly than intermediate rocks. Mafic rocks usually weather into dark-brown, reddish-brown, or orangish-brown colors--and dunite usually weathers into a yellowish-brown or brown color.
Hello Rock People! This is Dave the Geology Dude! Identification notes for this rock are below in this text. Please be aware that the only way to really learn rock identification, is to have hands-on experience. This is because visual experiences alone do not show properties like hardness, acid reactivity, density, and the range of variables that are common to each rock type. Don't forget that Geology isn't rocket science--it's Rock Science! Please "like" and subscribe to this YouTube channel!
Identification information for this rock:
1) color: andesite usually has a range of medium-gray colors. Note that andesite can be either slightly darker, or slightly lighter, than medium-gray.
2) grain size: porphyry--which is both coarse and fine grain size
3) hardness: generally about as hard glass (for unweathered, clean samples). Note that hardness tests usually are oriented to pure minerals--and not to rocks. This is because rocks usually contain a variety of different minerals (that individually may create different localized areas with different hardnesses within the rock). So, hardness tests usually are not performed on rocks that contain a mix of minerals.
4) composition: andesite is intermediate. So it contains a microscopic combination of plagioclase, hornblende, and biotite.
5) acid reactivity: does not react to acid
6) classification: it is an extrusive, intermediate igneous rock (volcanic)
7) density: it is about as dense other igneous rocks. Note that some types of andesite may contain areas with many vesicules or bubbles--which may affect density. But if an intermediate rock contains almost all vesicles, (which causes a much lower density rock than normal)--then that rock is probably a pumice--and not an andesite. Note that pumice can be either intermediate or felsic in composition.
8) environmental association: typically is found along subduction zone volcanic areas
9) summary: if a rock is medium-gray in color, and does not react to acid contact, or contain fossils, or contain layers--then it is probably an andesite. Again, the rock may have to be broken to observe the interior color and minerals.
Music (Youtube Audio Library): Get Tough (by TrackTribe)
Copyright by David Knoblach, 2023. All rights reserved
10 ماه پیش
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