by Dirtman » Fri Oct 26, 2007 9:04 am
A scale comes to mind. :-) Sounds sarcastic but it isn't. It'll be difficult to determine the precise volume unless you use displacement (unless it's cut stone).
It also depends on the type of rock and the minerals it's comprised of. All weights are approximate but solid granite weighs 168 pcf (pounds per cubic foot), limestone weighs 163 pcf and marble weighs 160 pcf. You could probably use 165 as an average weight but it won't be close if it's odd rock such as pumice (40 pcf) or magnetite (315 pcf).
A scale looks better all the time. :-) You can always weigh a small piece and use the weight to volume ratio to calculate a large piece.