In the northern part of Shilo Village is one of only two locations of gem rocks in the entire RuneScape world. The second is in the Lunar mines. Like regular mining, they require a pickaxe to mine, and they respawn in the same fashion. When mining a gem rock, there is a chance that you will receive one of three semi-precious gems: jade, opal or red topaz; and regular gems like sapphire, emerald, ruby, or diamond. The closest bank is in the southern part of Shilo Village. You need to do the Shilo Village quest to enter. Also note that the higher your mining level is, the better chance you have to get the higher level gems such as diamonds, rubies, sapphires, and emeralds.