Pumice

Pumice is a volcanic rock that floats on water. It forms when lava full of gas cools so quickly that the bubbles are trapped inside, leaving a stone that is mostly hole, with some rock around the edges to hold the hole together.^[1]

Other rocks regard floating as showing off. A rock, in their view, should go to the bottom and stay there, as rocks have done since the beginning of rocks.

Classification

Because a typical piece of pumice is more hole than rock, the International Rock Board debated in 1974 whether it was a rock with holes in it or a collection of holes with a rock problem. The vote was tied, and the minutes, which had been written on pumice, floated away before they could be signed.^[2]

Floating

Pumice floats because, holes included, it is lighter than the water it pushes aside. It sinks eventually, when the holes fill up with water and it remembers what it is. Rafts of floating pumice from undersea eruptions can cover hundreds of square kilometres of sea, and are the closest thing rocks have to a holiday.^[3] A boulder has never been on holiday, and says it does not see the appeal.

Uses

• Removing hard skin from feet, a job pumice did not apply for.
• Stonewashing jeans, in which jeans are washed with stones so that they look as if they have been washed with stones.
• Garden soil, where it improves drainage by being mostly somewhere for the water to go.

See also

• Rock (rock) – sinks, like a professional
• Pebble – also goes to the beach, but stays put
• Water – what pumice is on top of

References

1. Basalt, B. (1988). Mostly Hole. Magma Books. p. 1.
2. International Rock Board (1974). “Rock, or Holes?” Minutes lost at sea.
3. Float, F. (2012). Rocks on Holiday. Raft Press.