The Life Crystal is an item dropped after breaking a Heart Crystal. It is used to increase the amount of maximum Life the player has. When this item is consumed, it increases the player's maximum HP by 20 (one heart) up to a maximum of 400 (which requires 15 hearts). Additional Life Crystals collected can be used to make Heart Lanterns. To get higher amounts of health, one must collect Life Fruit in the Hard ModeJungle.
Obtaining and using a Life Crystal is required to get the NurseNPC.
A common way to quickly get max life is to create multiple worlds to gather Life Crystals.
In the Alpha version of the game, Eye of Cthulhu used to drop a single Life Crystal on death. This has been changed in the Beta version.
If one somehow manages to attack a monster with a Life Crystal (use it while close to a monster) it will do 1 damage.
It is likely that Heart Crystals and the Health Bar could be a reference to Heart Containers and the health bar in the Legend of Zelda franchise, seeing that the health bar in Zelda looks identicalin Terraria, and Zelda and Terraria use heart shaped items to increase health. Also, Terraria uses 16-bit graphics for the game as well as Nintendo's Super Nintendo Entertainment System having the same set of graphics, where Zelda: A Link to the Past is played on the SNES system
It is possible to spam Life Crystals on the mobile version of Terraria. To do this, players can simply use the item and, right before it disappears, place it in their inventory.