Item Crystal

From the Super Mario Wiki

An Item Crystal is an object found exclusively in the game Super Mario Galaxy. It is a three-layer crystal that can be found in multiple areas of the game, mostly on the first few stages and sometimes near bosses.

During the introductary cut-scene, the Airships are shown shooting crystal bits at Toads, making it a possibility that Bowser's fleet is the source of the other crystals in the game. Item Crystals have fairly weak structures and can be shattered using Mario's Spin move; inside them are items such as Coins, 1-Up Mushrooms, and the occasional Boost Star or Life Mushroom. Most of these crystals contain Star Bits of which Mario can later feed to Hungry Lumas; some may even contain Lumas or Toads, who help the player out once they are freed. The quantity of Star Bits obtained will average from three to ten, and most of the Item Crystals found throughout the game will contain four to six.