Gems can be obtained from mining, trading with other players, and as occasional monster drops. Using the Crafting skill, uncut gems can be cut, combined with precious metals to make jewellery and then enchanted using the Magic skill. Gems can also be cut into gem bolt tips. Wearing a charged Amulet of Glory increases a player's chances of unearthing a gem while mining. However, one does not receive any additional Mining experience if one manages to mine a gem in such a fashion. Note: It has been confirmed that, even as a free player without any amulet, you can obtain multiple gems of different kinds at one time from mining (at least two), but this is extremely rare. In such cases, members wearing a ring of wealth may potentially obtain four or more gems from mining one rock, though this is an even rarer occurence. Furthermore, though uncommon, it is possible for a free player, whilst mining a rock and competing with another for its ore, to lose the ore to the other player, but manage to find a gem all the same.
Any regular mine rocks (clay, copper, iron, coal, etc.) have 1/282 chance to retrieve a gem (sapphire to diamond) when mining (without an amulet of glory). It's even possible to mine multiple gems from the same rock.
The statues in Bandos's throne room frequently drop cut gems from sapphire through diamond, making the room popular for some gem hunters who can kill the statues easily. Completion of The Chosen Commander is required for access to the throne room.
Gems can also be mined from the gem rocks in the north-west corner of Shilo Village, Lunar Isle Mine, occasionally in Tai Bwo Wannai Cleanup activity, and also in gem rocks in the Al Kharid mining site resource dungeon. Gem rocks contain, in order of descending probability, opal, jade, red topaz, sapphire, emerald, ruby and diamond.
You can also obtain 8 sapphires from mining sapphire rocks in the cave found in the quest The Tale of Muspah quest. However, the rocks can only be mined once, so the sapphires do not respawn inside the rocks.
The original free version gems were officially released in the crafting update in May 2001. In March 2001, Jagex made gems appear while mining, although it was unintentional.
With the release of Divination, gems can now be automatically banked with the use of sign of porters. All gems found when mining gem rocks, ores, and even stars will be teleported when a porter is activated and worn. This is useful when mining rune ores while using a portent as it will not take away an inventory space, just one charge from the porter.