Pumice

volcanoes · rocks · geology

Born from volcanoes. Pumice forms when lava with lots of gas bubbles cools down really fast, trapping all those air pockets inside. This makes it look like a sponge made of stone.

Lighter than water. Pumice is so full of air holes that it can actually float on the ocean for years before eventually sinking. Scientists have even tracked pumice floating across entire oceans after volcanic eruptions.

Usually light-colored. Most pumice rocks are white, gray, or light tan because of what minerals make them up. This makes them easy to spot on beaches where they sometimes wash up.

Volcanic glass inside. Pumice is made of volcanic glass, which forms when lava cools so fast that it doesn't have time to form crystals. Sometimes you can see tiny crystals mixed in with the glass.

Different from scoria. Scoria is another volcanic rock that looks similar but is darker, denser, and has bigger air pockets with thicker walls. Pumice's tiny pockets and light weight make it unique.