Most mining stocks are/become penny stocks. The one exception is diamonds (and to a lesser extent, gold), because owners control the supply to market, keeping the price up. However, for consumer commodities (like coal, iron, aluminum, uranium, etc.) it isn't likely that the supply will be limited so prices plunge and are kept low. The lone exception to that recently is oil, because the world supply of easily obtainable oil is dwindling; new oil finds require more expensive drilling, which keeps the price up (not to mention oil commodities speculation).