Mining is checked when using a shovel or pickax to mine ore, stone, or sand, when using a shovel to dig up a treasure chest, and when smelting ore into metal ingots.
Mining for Ore Edit
When mining ore, every success results in two large ore. One large ore weighs two stones. Colored ore is supported on this server. See UOGuide for more details. It took me (qbradq) about four hours to GM mining from 0.0 real skill (20.0 displayed due to 100 str). In that time I mined 3774 large piles of ingots.
As you achieve higher mining skill as you mine you will have different gems appear in your backpack.