Reticulite tephra collected from Napau Crater, Hawaii Volcanoes National Park. This unusually large block (tephra >6.4 cm in diameter) of reticulite was erupted during one of the high lava-fountain episodes of the Pu`u `O`o cinder and spatter cone between 1983 and 1986. Pu`u `O`o is located on the east rift zone of Kilauea Volcano. See summary of Pu`u `O`o eruption.
Reticulite is a type of pumice that only forms during eruption of basalt lava by vigorous lava fountains. It consists of fragile volcanic glass that has cooled incompletely around the walls of gas bubbles. The bubbles formed during the "explosive" eruption of basalt lava. The porosity of reticulite can reach 98 percent -- so high that reticulite sinks in water.
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Last modified: October 15, 1998