cinders

Cinders are a type of volcanic tephra consisting of small, partially fused fragments ejected during explosive volcanic activity. In geology, cinders are typically classified as lapilli, with a particle size range of about 2 to 64 millimeters in diameter. They form when molten lava droplets are expelled into the air and solidify as they fall, or when surface lava shatters and quenches in flight.

Most cinders are vesicular and glassy, giving them a lightweight, porous texture. Their composition is usually basaltic to andesitic, though colors can vary from red or brown to black depending on oxidation and mineral content. The particles are often rounded or semispherical, with a rough, pumice-like surface.

Geologically, cinders accumulate around volcanic vents to build cinder cones, which are steep-sided, conical volcanic structures formed from successive eruptions that deposit alternating layers of ash and lapilli. Cinder layers serve as important tephra markers in volcanic regions and help scientists reconstruct eruption histories. They are typically found in volcanic fields and near Strombolian-style eruptive activity.

In everyday language, cinders can also refer to the residue left from burning fuel, such as coal or wood, in a furnace or fireplace. Historically, cinders have been used as a construction and landscaping material, sometimes in blocks or as aggregate in early concrete products, though modern practice often uses other materials.