Currently diamonds are pathetically worthless. Can we up their value, call them blood diamonds and give them their own gathering spot? Then make them only sellable at rebel outposts.
Sand should be gathered on a beach and then refined once into "silica sand" and then a second time into glass. This could then allow for an increase in value for glass.
With these two changes you can remove diamonds and sand from the quarry areas all the while making them more appealing to do.