An Uncut ruby is a red gem used in Crafting. At level 34 Crafting a player may cut an uncut ruby by using a chisel on it, which will grant 85 Crafting experience per stone, making the uncut ruby into a Ruby. Uncut rubies are generally more valuable as is, mostly due to the value of the crafting experience they generate.
Uncut rubies can be obtained in several ways. They can be generated randomly while the player is mining any sort of ore. Rubies are uncommon to rare drops from a multitude of monsters, and were previously offered as a reward from Random event gifts.
To obtain a ruby more directly, Players with level 40 mining who have completed the Shilo Village quest can try the gem rocks in Shilo Village. Gem rocks may also appear while playing the Tai Bwo Wannai Cleanup minigame, but these rocks are exhausted after 3 gems have been obtained. Note that gem rocks generate a random gem, not just rubies, so it may take several tries to actually obtain a ruby. It is also possible to obtain an Uncut Ruby from a Shooting Star. A slower way to get uncut rubies is cracking the Wall safe located in Rogues' Den. The final and only certain way of obtaining an uncut ruby is to use muddy keys to unlock the chest in the center of the lava maze, in high wilderness. This method is slightly hazardous, but it will always generate a ruby, as well as a handful of other rewards.
Being gems, rubies may be sold to the specialty Gem Stores found in Falador, west of the castle, and also to the gem trader in Al-Kharid. Doing so would be a complete waste, though, as these items are very sought after, being used to create many fairly valuable and/or useful other items.