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Scoria

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Scoria is vesicular and dark colored igneous rock that have or have not contain any crystals.  It is typically dark color, such as dark brown, black or purplish red. Most scoria is basaltic or andesitic in composition. The top of a lava flow is made up of a highly vesicular, rubbly material known as scoria. It has the appearance of vesicular lava. The formation of the rock when gases in the magma expand to form bubles as lave reaches the surface.The bubbles are then retained as the lava solidifies. Scoria is common in areas of recent volcanism, such as the Canary Islands and the Italian volcanoes. It is relatively low density due to its vesicles, bu it is not as light as pumice. Also differs from pumice in that it has larger vesicles with thicker walls. It has commercial use as a high-temperature insulating material. It also has applications in landscaping and drainage.

Name Origin: The word scoria comes from the Greek “skoria”= rust

Texture: aphanitic and vesicular (contains abundant large gas cavities)

Composition: intermediate (andesitic) to mafic (basaltic)

Color: black or dark brown

Cooling Rate: rapid, extrusive

Intrusive Equivalent: diorite or gabbro

Other Characteristics: vesicular like pumice, but denser and darker with larger vesicles

Origin: Extrusive/Volcanic

Mineral Composition: Predominantly Glass

Tectonic Environment: Divergent Boundary or Intra-oceanic hot spots

Comparisons: Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, and hence is denser. The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.

Scoria Composition

Scoria is a volcanic igneous rock. Also referred to as scoriaceous basalt, a term commonly used to indicate a basaltic pumice. It is commonly composed of approximately 50% silica and 10% calcium oxide with lesser contents of potash and soda. It is an extrusive igneous rock whose major minerals are plagioclase, pyroxene and olivine. Minor mneral contents may include apatite, biotite, hematite, hornblende, ilmenite, magnetite, and quartz.

It has a relative hardness of 5-6.

Scoria Formation

When the Scoria explodes, it consists of an explosive in the volcano, the excess gases and ash from the volcano. These gases are dissolved in the magma under extreme pressure. The magma from the volcanic eruption enters the air in which the pressure is released, and the magma solidifies when the temperature falls from the surface surface. When the magma solidifies, the gases in the melt are not released from the melt without solidification. These gases produce round or long pores. These pores were vesicles of rapidly emerging gas regions of melt solidification, otherwise gases would not be compressed.

The scoria from the explosion will be located near the mouth of the volcano and the heavy rock will fall down from the top of the volcano.

Where is it located

Scoria can be found in regions where Earth’s volcanic activity occurs. It is a ruthless rock filled with air bubbles ranging from black to dark red. The It is created as gas runs out of a volcano and the rock strikes around.

Scoria is gathered around the vents of a volcano. The cone-shaped hill formed by Scoria is called an ash cone. In some parts of the world, there are large areas with many cone cones called volcanoes. Scoria-producing volcanoes usually have short eruptions and are not very long. It is often used as a lightweight aggregate that is added to the landscape or to the concrete.

Scoria Uses

  • It is often used in landscaping and drainage works. It is also commonly used in gas barbecue grills.
  • It can be used for high-temperature insulation.
  • It is used on oil well sites to limit mud issues with heavy truck traffic.
  • The quarry of Puna Pau on Rapa Nui/Easter Island was the source of a red-coloured scoria which the Rapanui people used to carve the pukao (or topknots) for their distinctive moai statues, and to carve some moai from.
  • It is also used as a traction aid on ice- and snow-covered roads.

Scoria and Pumice

Scoria is a mafic volcanic glass. It is an extremely vesicular basaltic lava with very small (< 1mm) vesicles. Pumice is a felsic volcanic glass. It is rock foam with so much air in its structure that it often floats on water. Close examination of fresh pumice shows its glassy nature. Older, weathered pumice looses its glassy appearance (volcanic glass rapidly breaks down when exposed to water), but it is still lightweight and feels abrasive against the skin.

Conclusion

  • Magma containing abundant dissolved gas flows from a volcano or is blown out during an eruption results in the formation of scoria.
  • If molten rock solidifies before the gas escapes, the bubbles become small rounded or elongated cavities, which leads to scoria being produced.
  • The bodies that solidify in the air and become scoria produces ground cover all around the volcano vent with the heaviest deposits on the downwind side.
  • It has an angle of repose of 30 to 40 degrees, which is very steep due to the small volcanoes produced by brief eruptions with a vertical relief less than a few thousand feet.
  • Sometimes newly erupted lava flows contain abundant dissolved gas, and once lava starts to solidify, the trapped gas bubbles are the vesicles, and if the upper portion has an abundant number of vesicles, it is often called scoria.
  • Pumice is very similar to scoria that is also a vesicular igneous rock, but there are a few differences that can distinguish them.
  • It is usually always black or dark gray to reddish brown and pumice is white to light gray or light tan, due to their composition differences.
  • Pumice has a higher concentration of trapped bubbles allowing it to float, but thick walls of scoria make it heavy enough to sink.
  • Using a hand lens, a person can often see very tiny mineral crystals in scoria.
  • The production of lightweight aggregate is one of the main uses of scoria. It is crushed to the specific sizes and sold for a variety of uses.
  • Using concrete with scoria weighs about 100 pounds per cubic foot, but with typical sand and gravel it would weigh about 150 pounds per cubic foot.
  • The lighter scoria allows buildings to be constructed with less structural steel, and the air trapped in the scoria makes the concrete a better insulator resulting in lower heating and cooling costs.
  • Crushed scoria is used for ground cover in landscape projects, as a substrate in hydroponic gardening, and as roofing granules.
  • Buyers have the option of purchasing black, brown, or red material.
  • In addition, scoria may be used as rip-rap, drainage stone, or low-quality road metal. Small amounts of it can be used as sauna rock and as a heat sink in barbecue grills.
  • There are also scoria substitutes such as a lightweight aggregate that is produced by heating shale in a rotating kiln under controlled conditions.
  • Substitute scoria can have the same properties, appearances, and vesicles as the original, which is sold under the name “expanded clay,”, or “grow rocks.”

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Le Maitre, R. W. (2005). Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, 2nd Edition. Cambridge University Press.
  • Wikipedia contributors. (2018, November 15). Scoria. In Wikipedia, The Free Encyclopedia. Retrieved 01:38, May 12, 2019, from https://en.wikipedia.org/w/index.php?title=Scoria&oldid=868982411
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