pumita

Pumita, in geology, is the Spanish term for pumice, a light, highly vesicular volcanic rock that forms during explosive eruptions. It consists of a frothy mass of volcanic glass with numerous gas vesicles and is typically pale in color, ranging from white to light gray.

Pumita forms when viscous, silica-rich magma decompresses rapidly, trapping volcanic gases that create a foam-like structure. As the magma cools, the foam solidifies into a porous, glassy rock. Its composition is usually felsic to intermediate, with silica content commonly around 60–75 percent. Because of its high porosity, pumita has a very low density and can often float on water when freshly erupted.

Common properties include a rough, abrasive texture and a surface that can break into sharp edges. The rock is typically light in color, though mineral impurities can redden or darken it. Its vesicular network makes it a poor material for compact construction but valuable as an abrasive and as an additive in various applications.

Occurrences and uses: pumita is widespread in continental volcanic regions and is found in pyroclastic deposits such as pumice beds and ignimbrites. Economically, pumita is used as an abrasive (in polishes and cleansers), as a soil amendment to improve aeration and drainage in horticulture, and as a lightweight aggregate in construction. It is also employed in landscaping and as a natural abrasive in certain industrial processes.

Etymology: the term derives from Latin pumex, pumicis, with pumita representing the Spanish diminutive form. See also pumice, volcanic glass, and pyroclastic rocks.