This is called Pumice. It is formed when magma reaches the surface, and reduced pressure lets gas bubbles escape. When it cools, it has so many trapped air bubbles that it will actually float in water. What kind of rock is it?.

1. Igneous

   Yes! Igneous rocks formed from magma or lava. This is an igneous rock.

2. Sedimentary

   No. Sedimentary rocks are deposited by wind, water, ice, or gravity, and they often contain fossils. This is not a sedimentary rock.

3. Metamorphic

   No. Metamorphic rocks have been changed by heat and pressure from a different kind of rock. Instead of being changed, this got hot enough to completely melt, so it is not metamorphic.

4. Pumice is not a rock.

   No. Pumice is a naturally occurring solid that forms large layers in the Earth. Pumice is a rock.

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