cinder cone

or ash cone

Deposit around a volcanic vent, formed by rock fragments or cinders that accumulate and gradually build a conical hill with a bowl-shaped crater at the top. Cinder cones develop from explosive eruptions of lavas and are often found along the flanks of shield (gently sloping) volcanoes. Lava flows may break out of the cone, or they may flow from under the cone through tunnels. Cinder cones are common in nearly all volcanic areas. Although they are composed of loose or only moderately consolidated cinder, many are surprisingly long-lasting, because rain falling on them sinks into the highly permeable cinders instead of running off down their slopes and eroding them.

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Mineral deposit with a porous or vesicular texture (having small cavities). Siliceous sinter is a deposit of opaline or amorphous silica that occurs as an incrustation around hot springs and geysers and sometimes forms conical mounds (geyser cones) or terraces. Calcareous sinter, sometimes called tufa, calcareous tufa, or calc-tufa, is a deposit of calcium carbonate.

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A cinder is a pyroclastic material. Cinders are extrusive igneous rocks. Cinders are similar to pumice, which has so many cavities and is such low-density that it can float on water.


The following geologic characteristics define a cinder:

  • Uncemented
  • Vitric
  • Having bubble-like cavities, called vesicles
  • Measuring not less than 2.0 millimeters in at least one dimension
  • Apparent specific gravity between 1.0 and 2.0
  • Typical cinders are red or black in color.


Cinders have been used on track surfaces and roads to provide additional traction in winter conditions. Cinders are also popularly employed as inorganic mulch in xeriscaping, because of excellent drainage properties and resistance to erosion. In this context, they are referred to frequently with the synonym "lava rock".

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