What is this picture?

Question

What is shown in this image?

Accepted Answer

pumice stone surface. Pumice stone is so incredibly porous and lightweight that it can actually float on water for years, which is why geologists sometimes find pumice from volcanic eruptions thousands of miles away washing up on distant beaches. A single piece of pumice can contain so much trapped air that it has the same density as a cork, making it one of the few rocks that won't sink.

Answer: pumice stone surface