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Answer to Jeff's photo question

the brown rock looks to be brown chert. the reason it is shaped angular like that is because it was broken off the source rock and transported by water, then deposited not far from the source, perhaps in a landslide or flood. the angles aren't very sharp so it had to have been transported; if it were completly round this would mean it was transported a long distance in water. hope that helps

as for the rounded rock, my first guess is a rounded pebble of pegmatite, which is common in south dakota. my second guess is that its a geode or agate maybe? i have a cut geode that the outside looks almost exactly like that. sorry i cant be more helpful

From Rene - March 05, 2010 at 08:43:34

Message: 68820



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