Uncut gem
An Uncut gem is a gem that hasn't been cut. You can get these from mining ores or random events. Uncut gems are also a frequent drop from a variety of monsters. Generally sapphires, emeralds, rubies or diamonds are dropped by monsters, or are given away at random events. Most of the time when you get gems, they will be uncut. This way, you can cut them to get Crafting experience.
Uncut gems can be mined from the Gem Rock in the north-west corner of Shilo Village, Lunar Isle Mine and sometimes in Tai Bwo Wannai Cleanup minigame. You can only mine gems on a member's world. It is also possible to steal gems from the safes in the Rogue's den.
Uncut and cut gems can be purchased from, stolen from, or sold at a gem shop. They can be identified with a red gem 
icon on the World Map. There is one in Al-Kharid, one in Ardougne, one in the TzHaar City, and one in Falador.
Gems
Free-to-play
Requires 20 Crafting, gives 50 Crafting experience.
Requires 27 Crafting, gives 67.5 Crafting experience.
Requires 34 Crafting, gives 85 Crafting experience.
Requires 43 Crafting, gives 107.5 Crafting experience.
Pay-to-play (Members)
Requires 1 Crafting, gives 12 Crafting experience.
Requires 13 Crafting, gives 20 Crafting experience.
Requires 16 Crafting, gives 25 Crafting experience.
Requires 55 Crafting, gives 137.5 Crafting experience.
Requires 67 Crafting, gives 167.5 Crafting experience.
Trivia
- Uncut gems used to have the examine text "It would be worth more cut" but it was changed since uncut gems are generally worth more than cut ones.
- You need a higher crafting experience to cut ruby than sapphire, but in real life, ruby and sapphire are just different varieties of corundum.
- It is possible to mine two uncut gems from one rock in one attempt, usually a sapphire and something else.