A Heart Crystal is a red heart-shaped stone that can be found underground. A Heart Crystal is only breakable with a Pickaxe or Drill. When broken, a Heart Crystal will drop one Life Crystal. Occasionally, the Heart Crystals will spawn in groups of 2 or even 3 close to each other.
Heart Crystals cannot be obtained by breaking the blocks under them, and the two blocks it is on cannot be broken until the heart is gone.
The number of Heart Crystals in a world depends on the size of the world: there will be about 20-30 in small worlds, 30-35 in medium worlds, and 40-45 in large worlds.
When lava flows over one of these tiles, it will break and drop a Life Crystal.