hyaloclast

plural hyaloclasts

1. geographyA volcanic glass fragment formed by hot lava rapidly cooling when it encounters water or ice, causing it to shatter into small, glassy pieces.

   Hyaloclasts occur partly between the individual lava flows, partly in the vents penetrating the volcanic formations.

   1974, Acta Geologica, volume 18, page 388

   1 more example

   Suite IV represents sediment gravity flow deposits near a deep submarine vent, whereas Suite V represents a mixture of hemipelagic mud and epiclastic sand which incorporated some hyaloclasts.

   1987, Brian J. Taylor, N. F. Exon, Marine Geology, Geophysics, and Geochemistry of the Woodlark Basin-Solomon Islands (page 300)