Pumice develops in lava
which is rich in gases and viscous. The gases, released because of a
sudden diminution of pressure at the Earth's surface, create the many
cavities. Shortly afterwards the lava solidifies. Since acidic lavas
are especially viscous they are favorable for the formation of pumice.
Accordingly most pumices have a high silica content and light colors.
They are thus assigned to the rhyolite family. |
