You can sell sparkly at any 70% or 80% vendor - you'll get the same for them, 6 currants a piece. However, recommend selling gems either in auctions or at the 80% tool vendors. Never sell to mining vendors...I think they only buy at 50%, and never buy from mining vendors since they have a large markup for most things. Though I know a lot of folks like to donate gems to the shrines.
I also like to mine dullite (the cheapest of the rocks), since there are times when it sells well in the auctions (as much as sparkly at the vendors), but you have to watch the market fluctuations (since sometimes the postings can be pretty low)...but at high volume playing times, sometimes dullite is easier to find than sparkly since everyone likes to mine sparkly.
Mine Sparkly and Metal.
Smelt the Metal into Ingots.
Crush the Sparkly into Elements.
Rub the Ingots into Molybdenum Ingots.
Craft the Molybdenum Ingots into Crystalmalizing Chambers.
Sell the Crystalmalizing Chambers to the Tool Vendor in Cebarkul.
Note: You will accumulate extra Red, Green and Blue Elements. You can rub these into other Ingots (Copper or Tin) and craft Super Scrapers or other things; or you can, with a Test Tube, experiment them into Compounds to donate at Shrines, or turn into Powders, or sell.