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Post by snowmom on Jan 5, 2015 6:33:39 GMT -5
and become something else? Got pictures to add ? The bright pink upper left is melted together and the black areas seen in it are all translucent and would probably polish up sort of grey. The big green sphere with the yellow spot is the most melted, but you can see it probably had its roots pretty close to granite. If the matrix is melted, does it then become porphyritic, or something else? Most of the others here do not have individual crystals as matrix, but melted material which may have been granite granules once, or never quite made it. All very interesting and sort of confusing Do you have photos to add? Looking for a little bright color on a cold northern morning.
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on Jan 5, 2015 8:41:11 GMT -5
Good question but I am as ignorant as you are. I have some pretty pink granite and it does not look anything like those. Jim
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alan
starting to spend too much on rocks
Member since December 2013
Posts: 111
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Post by alan on Jan 5, 2015 9:34:35 GMT -5
Granite is technically defined by chemical composition. It ceases to be granite when it is altered by weathering into sedimentary rock or thermally altered into a metamorphic rock.
Edited: Tapatalk autocorrected?
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alan
starting to spend too much on rocks
Member since December 2013
Posts: 111
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Post by alan on Jan 5, 2015 9:40:14 GMT -5
Porphyritic just describes the crystal texture... It can apply to igneous rocks of various chemical composition.
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Post by deb193redux on Jan 5, 2015 9:56:16 GMT -5
if heat or chemistry alters it into metamorphic rock, then it is not a granite. but if it was a courser grained igneous rock that cooled below the surface (not extruded) then it is a granite.
"course" is a broad category and some granites are much finer grained and more homogeneous than others.
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Post by Pat on Jan 5, 2015 10:27:02 GMT -5
Good question, snowmom. When granite morphs into something else, what is that called? Is there more than one "that"?
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Fossilman
Cave Dweller
Member since January 2009
Posts: 20,688
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Post by Fossilman on Jan 5, 2015 11:05:31 GMT -5
Interesting question,yes! Liking the answers too......
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Post by deb193redux on Jan 5, 2015 11:12:58 GMT -5
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Post by 1dave on Jan 5, 2015 11:34:16 GMT -5
The earth is a huge recycling plant. Stuff gets hot and melts. Light stuff floats, heavy stuff sinks. Stuff churns and gets mixed up. Elements do their thing and minerals have specific rules. At specific temperatures and pressures they have to take a specific crystal shape and drop out of the mix. Heavy rocks contain little silica and becomes basalt Lighter rocks have more silica and become andesite with lots of feldspars Even more silica has quartz crystals and becomes granite. The quartz weathers into sand Feldspar becomes clay Spinning wheel got to go round.
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bsky4463
fully equipped rock polisher
Member since September 2013
Posts: 1,696
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Post by bsky4463 on Jan 5, 2015 13:20:43 GMT -5
Another top shelf reference from 1dave.....many thanks! Cheers.
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spiritstone
Cave Dweller
Member since August 2014
Posts: 2,061
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Post by spiritstone on Jan 5, 2015 17:56:56 GMT -5
The earth is a huge recycling plant. Stuff gets hot and melts. Light stuff floats, heavy stuff sinks. Stuff churns and gets mixed up. Elements do their thing and minerals have specific rules. At specific temperatures and pressures they have to take a specific crystal shape and drop out of the mix. Heavy rocks contain little silica and becomes basalt Lighter rocks have more silica and become andesite with lots of feldspars Even more silica has quartz crystals and becomes granite. The quartz weathers into sand Feldspar becomes clay Spinning wheel got to go round. This material you post is all fantastic to read. I bought some of the African sunstone and cabbed one up. The copper coloring inside is kinda cool. Thought the cab was a little boring and tossed into my "maybe someday" pile after it was done.
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