what is the only rock that floats

The only rock that floats is pumice, a light and porous volcanic rock formed when lava cools quickly above ground. Pumice is filled with gas bubbles that are trapped inside the rock, making it less dense than water and allowing it to float. Pumice can form miles-long debris patches on the ocean known as pumice rafts that can travel for thousands of miles, and it can help scientists discover underwater volcano eruptions. Pumice is also rich in nutrients and serves as a means of maritime transport for many plants and other organisms.