Gems (currently just Rubies, Sapphires, and Emeralds) are added by RedPower. The only use for them (with the exception of Emeralds, which can be used to make the Sonic Screwdriver) is to make tools with the speed of diamond tools but a durability of just 500, which is less than iron. They cannot be crafted into armor. An Iron pickaxe or better is required to mine gems.
Each gem is worth 1024 EMC, making for a nice source of EMC, as the ores are rather common.
The Tekkit Emerald is not the same as the vanilla Emerald and cannot be used to trade with villagers as of Minecraft version 1.3.2.
Every Gem is used to make the following items: Pickaxe, Axe, Shovel, Sword, Hoe, Sickle, Handsaw, and a Gem Block of their respective type. The only exception to this is the Emerald, which is used to craft the Sonic Screwdriver.
Each of these are made with the same pattern as the the vanilla versions, but using gems rather than materials like iron and diamond. Like the vanilla tools, these are all enchantable. Sickles and Handsaws can also be created using gems.
- In Tekkit Lite and Technic Pack, the Emerald has been renamed the Green Sapphire because an emerald already exists.
- In Project Red, the Emerald has been renamed the Peridot because an emerald exists.