* = Base: is the minimal value, intrinsic or perceived, of a particular gemstone, whether precious or semi-precious. Two examples:
#1: the Turquoise --- in some regions of Earth, it is a precious stone, in others, it is merely semi-precious, though of higher status than say, quartz. Because of this diverse cultural valuation, turquoise will never have as high of a minimal base than my second example...
#2: the Diamond --- actually Emeralds should be more valuable (and maybe are, now; for diamonds are proving to be "common as dirt", to use the vernacular) since emeralds are now found to be rarer to find than diamonds ever were. That being said, "perceived value" has kept diamonds at the forefront of monetary valuation bases of all the gemstone types.