Is the amount of sand finite?

Once you dig out all the sand, it will never respawn. You are guaranteed to have at least 100 sand tiles on a map (any map having less is rejected and regenerated).

Here are the minimum amounts of tiles for each level:

• Overworld:
  • Rock: 100
  • Sand: 100
  • Grass: 100
  • Tree: 100
  • Stairs Down: 2
  • Stairs Up: 2 (As determined by the Sky)
• Cave level -1:
  • Rock: 100
  • Dirt: 100
  • Iron: 20
  • Stairs Down: 2
  • Stairs Up: 2 (As determined by the Overworld)
• Cave level -2:
  • Rock: 100
  • Dirt: 100
  • Gold: 20
  • Stairs Down: 2
  • Stairs Up: 2 (As determined by the Cave Level -1)
• Cave level -3:
  • Rock: 100
  • Dirt: 100
  • Gem: 20
  • Stairs Up: 2 (As determined by the Overworld)
• Sky
  • Cloud: 2000
  • Stairs Down: 2