The Rock - Scoria

  • Igneous Rock Type: Extrusive
  • Related to:  Basalt, obsidian, pumice
  • Chemistry: Basic to intermediate
  • Color: Black, brown to red
  • Texture: Glassy
  • Origins: Volcanic lava flows and ejecta
  • Common Minerals: N/A
  • Accessory Minerals: N/A
  • Uses: Decorative stones, grilling stones

Scoria is a textural rock type and not a rock that is classified by mineralogy or chemistry. It forms from lava that is rich in volatiles or gases but is less viscous than a pumice forming lava. When the molten rock is rising in the volcanic pipe, gases begin to form and collect and those gases form large bubbles in the lava. The resulting solidified rock is scoria. Although the open spaces in scoria can be large the rock is generally heavier than water, unlike most pumice which can float on water.

Some scoria forms from lavas that flow out of a volcano and some scoria can be pyroclastic. Pyroclastic rocks form from lava that is ejected from the volcano. Scoria (which is also known as cinder) is the primary component of cinder cones. A cinder cone is a small but very common volcano type. Cinder cones have also been called scoria cones. Cinder cones rarely grow very large, but form sometimes very symmetrical cone-shaped hills.

Scoria does not have a lot of uses. In fact the name is derived from a term for waste. However it can be used as an interesting decorative stone with some reddish color. Some of the large Easter Island statues called Moai have scoria stone in their designs.

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