It’s about time. We are now on Instagram!
glassy igneous rocks low in silica, such as basalt or diabase. Tachylytes are black with a pitchlike or resinous lustre; in thin sections they are characteristically brown and translucent, and the glass is crowded with granules of magnetite. Tachylytes are found only under conditions that imply rapid cooling, and they are much less common than are the corresponding acid volcanic glasses, principally because of the greater fluidity and greater tendency of basic lavas to crystallize.