PRECIOUS STONES.	101
	commonly curved; the true explanation of this is a matter of uncertainty. The great majority of minerals which are found crystallised occur bounded by true planes, but on the other hand a few, and prominent amongst these few is the
	Diamond, are more often found in curved forms. Still more interesting perhaps is the fact that certain crystallised minerals may have the majority of their surfaces quite flat, yet some one or two crystal forms of the same mineral may almost constantly be found curved; the writer, in the