This is called a 'heartstone'. It is a huge blue gem taken from the body of a fallen Ma'Xeochicatl. It wiggles slightly and is cool to the touch. The uses for this gem are not widely known.

Drop it on the ground in a combat area, wait a couple minutes, and voila a Ma'Xeochicatl.

Used for rented rooms.

How do I rent a room?