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MikeCarra
Guest
After observing this particular poster for a time, I pick number 3.
While I believe that gradyll is only interested in hearing those things which support his simplified view of science, and will go to whatever extremes he needs to (ranging from merely ignoring those things he doesn't like/understand to borderline libel of other posters) there is a 4th option.
Gradyll is, technically correct, when he points out that there is PHYSICAL weathering of igneous rocks. He points to "freeze-thaw" which can exploit fractures and cracks.
What he fails to do (and he thinks that this failure is his hypotheses' "salvation") is to take into account that just about ANYTHING that is attacking the granite will be MUCH MORE EFFECTIVE attacking the nearby softer sedimentary rocks.
Grady is sowing "doubt for doubt's sake" again. It is only important for him to find a means of breaking down igneous rocks. Then his work is done.
This is understandable from someone who clearly hasn't even darkened the door of an intro geology class (that's actually kinda sad because a Geology 101 class is fun and usually pretty easy).
Here's a few pointers:
1. The surrounding rocks in the Spearfish Fm appear to be mostly siltstones and sandstones along with a layer of gypsum (the latter being a very soft mineral). Siltstone and sandstones are usually little grains cemented together so can be relatively friable (meaning they can break apart)
2. Devils tower is an igneous rock called a PHONOLITE which contains a lot of feldspathoids and feldspars (mohs hardnesses 5-6 or so) along with other minerals.
Yes BOTH will weather through physical processes. NO: THEY WILL NOT WEATHER AT THE SAME RATE. THE PHONOLITE WILL HOLD OUT LONGER.
It's a matter of rate (along with a bit more mineralogy)
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