If you don't like granite, the next most efficient option would likely be powermining iron. A spot far away from the bank is good, and ideally you would take almost a full inventory of urns with you. Don't forget to activate them by adding an earth rune. Then you just mine and drop ore, and the urns fill up as you do so, and you can teleport them as you wish. You can also take advantage of Divine Locations and use your daily quota on mining rocks that people place to gain a little more xp, as well as the shooting starts D&D, if those might help a bit. If you are in a clan with a citadel of sufficient tier, you may be able to mine in there, which is semi-afk and also doubled xp over the weekend. It's perfectly possible to do it with mithril or gold ore instead if you like, but it will take quite a bit longer to accomplish.