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Scoria is a highly vesicular, dark colored volcanic rock that may or may not contain crystals (phenocrysts). It is typically dark in color (generally dark brown, black or purplish red), and basaltic or andesitic in composition. Scoria is relatively low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water. The holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (lapilli, blocks and bombs), for instance in Strombolian eruptions that form steep-sided scoria cones. Most scoria is composed of glassy fragments, and may contain phenocrysts. The word scoria comes from the Greek σκωρία, skōria, rust. An old name for scoria is cinder.
From the observatory, where His Majesty's faithful servant still remains, come telegrams that the great pebbles -- what we call scoria -- have ruined
Porcellanite (also called scoria or clinker) forms from the natural burning of coal beds; it caps the hills with distinctive red-orange rock.
There are tracts of these which are in part or wholly of volcanic origin; then the hills are called scoria buttes.
The eruption opened a 2,000ft fissure, and also produced lava fountains that built several hills of bubble-filled lava rocks, called scoria, along the vent.
But I was on a bladed road which the gas companies have recently covered with what they call "scoria".
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