Scoria is a frothy-textured, mafic extrusive igneous rock. It has an abundance of small holes formed by trapped gas bubbles during solidification of volcanic lava. The solid portions of scoria can be glassy or finely crystalline (aphanitic). If a scoria's solid portions are not glassy, the material typically has the same mineralogy as basalt. Another term for many scorias would be scoriaceous basalt. Some scorias are intermediate in chemistry (but still dark in color), and are better named scoriaceous andesites.
Fresh scoria is typically black to dark gray in color. Weathered/oxidized samples tend to be brownish and reddish in color. Most scorias are a bit too dense to float in water, but there are exceptions.
Scorias are relatively common landscaping rocks around many restaurants and businesses.