Science, Maths & Technology
Pumice
...out more about The Open University's Science courses and qualifications Pumice is a fine-grained volcanic rock. It is very light grey to medium grey in colour. It contains a lot of empty gas bubbles, so it is very light and looks rather like a sponge. Sometimes pumice is so light that it will float on water. [Pummice] Pummice How is it formed? Pumice is formed when...