pumice - teaching hand specimen of unusual pink pumice
Pumice is a very cellular volcanic glass. The cells are spherical, tubular or irregular in shape. Most pumice is gray to white in color. The composition of this silica-rich volcanic rock is similar to that of obsidian or granite. Instead of slowly cooling underground, it was blasted from a vent and cooled almost immediately, trapping bubbles of gas. If this same lava formed a lava flow, the resulting rock would be rhyolite or obsidian, and if it had cooled slowly deep underground, it would have formed granite or a close relative.
This pumice is from the no-longer-active Insulating Aggregates mine in Chalfant Valley, Mono County, California. White pumice from the same mine was used for years as the scouring agent in Lava soap. It was also sold for soil amendment as Par-Ex Agricultural Pumice. The pumice was formed during the eruption and collapse of the Long Valley Caldera 700,000 years ago. It is embedded in a thick sheet of tuff, welded volcanic ash, from that eruption. At this locality the tuff is only slightly welded and the pumice weathers out.
The silica-poor equivalent of pumice is basalt scoria, though the gas bubbles are usually larger. Scoria and basalt are silica poor. A lower silica content makes lava less viscous so it readily fountains from vents. Loose pieces of scoria form any number of small cinder cone volcanoes in the western U.S. Both pumice and scoria are mined as decorative rock. Students will recognize scoria as "McDonald's flower bed rock.
Pumice varies in appearance and density. See also our specimens of white pumice and of gray to black pumice. If you are looking for pumice that floats like a duck, select the white pumice that we offer. This pink pumice will usually, but not always float.
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