Tephra

thumb|Kutkhiny Baty, a pumice rock formation outcrop located 4 km from the source of the Ozyornaya (Sea of Okhotsk)|Ozyornaya River (Lake Kurile), near the southern tip of the [[Kamchatka Peninsula, Russia]]

volcanic material formed during explosive eruptions with the diameter of the grains less than 2 mm

thumb|Volcanic tephra at Brown Bluff, Antarctica (2016)

volcanic projectile, recognisable later by shape

thumb|right|340px|Lapilli on Kilauea

thumb|Rocks from the Bishop tuff from California, United States, uncompressed with [[pumice on left; compressed with fiamme on right]] thumb|The caprock in this photo is the ignimbrite layer of the [[Rattlesnake Formation in Oregon.]]

Scoria or cinder (plural: scoriae) is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts. It is typically dark in color (brown, black or purplish-red), and basaltic or andesitic in composition. Scoria has relatively low density, as it is riddled with macroscopic ellipsoidal vesicles (gas bubbles), but in contrast to pumice, most scoria usually has a specific gravity greater than or at 1 and sinks or remains in place in water rather than float at the surface. However, some sco

cloud of ash and tephra released during an explosive volcanic eruption

250px|thumb|right|Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the [[volcanologist's hands is rhyolitic tephra from Hekla.]]

mountain in United States of America