davefoc
Philosopher
From wiki:
In geology, a boulder is a rock with grain size of usually no less than 30 centimetres (1 ft) diameter.
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It says nothing about minimum weight.
Excellent point. The rock found in the cottage that has been described here as about nine pound might have been a boulder by a technical definition if its density was low enough so that if it was one foot in diameter it would have weighed nine pounds.
The density of rock is typically about 150 pounds per cubic foot
A rock that is one foot in diameter made from typical rock (~150 pounds per cubic foot) would weigh about 78 pounds. So if the rock that was found in the cottage had a density of about 9/78 of normal rock (~17 pounds per cubic foot) then the rock might have been about 1 foot in diameter and met the definition from Wikipedia of a boulder. It seems unlikely from the photographs that the rock was actually one foot in diameter but if it had been then you would certainly be right that as per the Wikipedia definition it would have been a boulder.
I'm not sure what rock that might have been, but pumice weighs about 40 pounds per cubic foot, so it must have been an unusual kind of rock. Or maybe it was hollow.
On the other hand maybe you were just using a bit of hyperbole to emphasize the point that you think that throwing a nine pound rock (about 6 inches in diameter assuming typical rock density) through a window was some sort of feat requiring abnormal human skills and strength.
I continue to be surprised that you think this. I am a fat old man and I just went out in to the yard, found a concrete block that was about 15 pounds and heaved it about 15 feet with far less than all my strength. I think I'd have a pretty good shot at more than 30 feet with a nine pound rock.
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