Scoria

Common card · No. 231613

Scoria (pl. scoriae), also called volcanic cinder, 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. The geological term cinder is synonymous and interchangeable with scoria, though scoria is preferred in scientific literature. Scoriae have relatively low densities, as they are riddled with macroscopic ellipsoidal vesicles (gas bubbles), but in contrast to pumice, most scoriae usually have specific gravities of at least 1 and sink or remain in place in water rather than float at the surface. However, some scoriae can have densities similar to that of pumice, especially if they are unusually porous and have small and abundant vesicles, and will float in water. Scoria with larger vesicles and thick walls can also float if the vesicles are not interconnected. Fragments...

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