Scoria

Scoria is a dark, vesicular volcanic rock formed when gas-rich lava cools. It is generally denser and less silica-rich than pumice.

Vesicle (geology): A cavity in volcanic rock formed by gas bubbles in molten lava. Its abundant gas-cavity spaces give scoria its characteristic porous texture.
Volcanic eruption: The release of magma, gas, and other material from a volcano. Scoria forms when gas-rich lava erupts and begins cooling at the surface.
Cinder block: A concrete masonry unit made with lightweight aggregate, historically including volcanic cinders. Scoria can serve as lightweight aggregate in masonry blocks.
Cinder cone: A steep, usually small volcanic cone built chiefly from loose pyroclastic fragments. Many cinder cones are built largely from scoria thrown out around a vent.
Tuff: A rock formed when volcanic ash and other fine pyroclastic material become compacted or cemented. Unlike scoria’s individual vesicular fragments, tuff forms from consolidated volcanic debris.
Basalt: A dark, fine-grained volcanic rock low in silica and rich in iron and magnesium. Scoria commonly forms from basaltic lava, though its texture sets it apart.
Exsolution: The separation of a dissolved component from a fluid as conditions change. As magma rises and pressure falls, dissolved gases separate and form bubbles.
Lightweight aggregate: A low-density granular material used to reduce the weight of concrete and other products. Scoria is a naturally occurring source of lightweight construction aggregate.
Parícutin: A Mexican cinder cone volcano that emerged in a farmer’s field in 1943. Its rapid growth produced extensive deposits of scoria around the cone.
Volcanic bomb: A pyroclastic fragment larger than 64 millimeters that was molten or plastic when ejected. Large scoria fragments may be bombs, but the term describes size and eruption state.

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