#mystic stone

I'm trying to figure out the best way to get a prizzie without going into skull cavern for a friend bc she HATES it. The wiki is super specific about the chances of a diamond node spawning in the Mines, but it only says that mystic stone chance is "increased by mining skill and daily luck". Does...

Can you find mystic stones not in the quarry? I found only one at the quarry, is there other places?. They have a 25% chance to drop a prismatic shard so that sounds good.