You are better off putting them up at the flea market part of ReTail and letting your villagers buy them for even more than Reese will give you.
Emerald, ruby, amethyst and saphire will get you 4,000 from Reese on a day when ore is on special. Villagers will pay 7,999 for each of those at the flea market. Silver and Gold will get you 9,999 each from the flea market but only 6,000 (silver) and 8,000 (gold) from Reese.
I sell all my ores at the flea market each day - it's a steady source of income. Same for the Superb Coffee Beans you get from working at the cafe. Villagers will pay 7,999 for those also.