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As getting dungeon groups can be a real pain in the proverbial my suggestion is that players could mine gems upto glim with random drops from cracked to glim level 1 - cracked, level 16 - cracked/jagged, level 24 - cracked/jagged/flawed, level 32 +fair, level 40 +glimmering(max gem)
With gems being random upto max, some people will grind this for higher levels to try and get glims but at the same times as gems wouldn't be guaranteed glim onyx for example this wouldn't be likely to be abused or replace dungeon runs. It just gives an opportunity for players not able to gather glimmering gems in other ways, a chance to gather them.