Pumice is a volcanic rock, but it had a lot of air in it while it cooled.

Chemical Formula: Varied
Class: Volcanic Igneous
Hardness: Varied
Coloration: Generally white or light gray, can be black

How to identify it/Unique Characteristics or Properties:
Pumice is a volcanic rock, the same composition as rhyolite, but had a lot of air in it while it cooled. This could be because it was in the air, falling from a volcanic explosion, or because the lava was bubbling a lot as it cooled. The air creates many pockets, making a very light rock with many holes in it. These can be tiny holes or large ones running straight through the pumice. Much of pumice can actually be glass, as it would have formed obsidian if it had remained under pressure.

Where to find it in…

The Northwest: Eastern Oregon’s lava flows have some good specimens, as does Hawaii.
Other: Wherever explosive volcanoes can be found.
Past Uses: It has been used to scrape off rough skin, or to sand carvings, etc. It can be used to polish and clean quite well.
How it was Made: Volcanic eruptions spew lava into the air, which cools in the air as it falls, leaving a rock with many tiny air holes in it.
Interesting Facts: Pumice is actually floats in water at first, but will eventually become waterlogged as water fills the fair holes, and it will sink.