Scoria is a type of igneous rock. Igneous rocks are rocks which solidify from molten material (i.e. magma). When magma cools, it can occur in two places - beneath the surface of the earth (plutonic) or on top of the surface (volcanic). Igneous rocks can be identified by the determination of the composition and texture of the rock.
The composition of scoria is mafic and its texture is vesicular. Mafic describes any silicate mineral or rock that is rich in magnesium and iron. The term is actually a portmanteau of the words "magnesium" and "ferric." Most mafic minerals and rocks are dark in color and have a relative density greater than 3. Vesicular texture denotes any volcanic rock characterized by having many cavities (known as vesicles) at its surface and inside. The vesicles form during the extrusion of magma to the surface. At the pressure decreases, magmatic gases are able to come out of the solution, forming gas bubbles in the magma. When the magma is extruded as lava and cools, the lava solidifies around the gas bubbles, preserving them as vesicles.
Interesting fact: The landscaping product commonly called "lava rock" is scoria
Another interesting fact: The cinder mix widely used on outdoor running tracks is made of scoria.
Other rocks that look similar to scoria are slag and pumice.
Sunset Crater in Arizona |