Pumice is indeed a volcanic rock that floats, and this is due to its low density.

While the exact density of pumice can vary depending on its composition and how porous it is, it generally falls within the range of 0.5 to 1.0 grams per cubic centimeter (g/cm³) .

For comparison, the density of water is 1 g/cm³. This means that pumice is less dense than water, which is why it floats.