pumice - pale pinkish tan pumice - large display specimen

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. This pumice specimen will float, though less like a duck and more like an iceberg. Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. It may not be instantaneous, since a human has to take a look and we might be out in the field during the day. A link in that invoice will bring you back to checkout, no hassle. It may not be instantaneous, since a human has to take a look - we might be out in the field during the day and won't see it until that night. Shipping: By Priority Mail or USPS Ground Advantage, whichever is cheaper, unless we find a better rate. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.