The names of the gems in this photo from left to right are:
Alexandrite, Amethyst, Aquamarine, Diamond, Emerald, Garnet, Opal, Peridot, Ruby, Sapphire, Topaz, and Zircon.

(Don't worry, I fixed it to be the default stone texture)
Each gem has it's own block. It can be crafted by placing nine gems on the crafting table as so:

As of 1.1, picks can be crafted as so:

They are slightly better than stone pick.
As of 1.2, gems are less common, and they can be made into axes:

They are better than stone.
Licence: WTFPL
Downloads:
Version 1.0: Broken
Version 1.1: Broken
Version 1.2: Download