Pumice: the Rock that Floats

     Have you ever heard the phrase, “sink like a rock?” I am sure that you have, and it makes sense, because most rocks are so dense that the idea of one of them floating would seem completely ludicrous. However, you will soon see that the phrase, "sink like a rock" does not ring true in the case of every rock.
     Pumice is a natural glass that is formed by volcanoes. When molten rock erupts from a volcano it can form a number of different rocks under different circumstances. Sometimes when this molten rock cools quickly it forms natural glass, a substance that is a lot like the glass that we use for making jars and windows, but is made by natural processes, like obsidian. Pumice is formed this way, but unlike obsidian, which is dense and has very sharp edges, pumice is filled with bubbles of gas and is very light. When this gas escapes the bubbles leave a lot of tiny void spaces in the rock and thus pumice is formed. Pumice has no regular shape, but is rather found as amorphous pieces of hardened lava-froth. Pumice is usually white or gray in color, but other color varieties do exist. The color of pumice really depends upon what kind of rock was melted to make it. Pumice that is composed mostly of rhyolite or trachyte is white, pumice that is composed mostly of andesite is yellow or brown, and pumice that is mostly composed of basalt is pitch-black. As I have said before, the bubbles found in pumice make it very lightweight. Pumice is so light, in fact, that it will actually float in water!
     Pumice is used to make gentle abrasives such as Lava Soap, a brand of liquid hand soap that contains small pieces of pumice that help to scrub grime off of one’s hands. You can buy blocks of pumice to remove calluses from your feet, as the porous volcanic glass will act as sandpaper against the dead skin while having no ill effect on your living tissue other than some minor discomfort. One interesting use for pumice that I have seen is as a landscaping stone. At the gardening section of a certain hardware store I once saw boulders of pumice for sale that measured about two feet across. They were supposed to imitate other sorts of stones in landscaping applications. These were somewhat comical, because while they looked like small boulders I could lift them with ease.
     Being a volcanic rock pumice can be found, theoretically, wherever volcanoes are present. There are large sources of pumice, however, which include: Italy, Turkey, Spain, Greece, and the United States in the Rocky Mountains and the Pacific Coast. Interestingly, pumice can sometimes travel far from its source. Since pumice can float on water for months before it becomes waterlogged and sinks, any pumice that was formed near the ocean can drift to wherever the currents may carry it. After the eruption of Krakatoa large pieces of pumice floated about in the Indian Ocean for months. The pumice from Krakatoa floating about in the ocean actually posed a hazard to ships for a little while afterword.
     Pumice is certainly one of the coolest rocks that I know of, after all, how many rocks do you know of that can float? Perhaps rock and mineral collectors can coin a new phrase, “sink's like most rocks.”