An igneous, or volcanic, rock that formed due to the rapid cooling of lava that has been exposed to the open air or near the surface, it features a glassy matrix that is interspersed with minerals. Usually grey to black in color, it is known to weather rapidly to a brown or red because of the oxidization of the iron-rich minerals that are contained within it.
It is typically defined by both its mineral content, and texture. It is called vesicular Basalt, Cinder, or Scoria, it may or may not contain crystals. The vesicles are formed as dissolved gases are exsolved, resulting in the formation of small, spheroids that open into one another. It looks like a dark version of pumice, another vesicular igneous rock, though vesicular Basalt has a higher specific gravity and will sink in water.
Origin: CO