Porphyritic Basalt Rock, 2 Pieces

Each Rock Measures Approx. 1-2 Inches in Length
by American Educational Products

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. Basalt that is porphyritic has large, well defined crystals set within a matrix of finer grained crystals that are not always visible to the naked eye, though there are clear differences in the sizes of the crystals that are visible. Each rock measures approximately 1-2 inches in length. 

Origin: CO, Canada