Crystal Shard

Crystal Shards are found in the Underground Hallow where they "grow" on Pearlstone Blocks, even when submerged in water or lava. Unlike most other resources that grow/respawn, Crystal Shards can grow in any direction (i.e. on ceiling and walls). They cast a faint glow, like Demonite Ore, are quite common and sell for good money. They are also used in the creation of several useful items (in particular, Crystal Bullets), so it is wise to farm them when possible. They can also be placed for illumination just like a Torch, though not quite as luminous.