Scoria

Scoria (Template:Plural abbr), also called volcanic cinder, is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts.[1][2] It is typically dark in color (brown, black, or purplish-red), and basaltic or andesitic in composition. The geological term cinder is synonymous and interchangeable with scoria, though scoria is preferred in scientific literature.[2][3]

Scoriae have relatively low densities, as they are riddled with macroscopic ellipsoidal vesicles (gas bubbles), but in contrast to pumice, most scoriae usually have specific gravities of at least 1 and sink or remain in place in water rather than float at the surface. However, some scoriae can have densities similar to that of pumice, especially if they are unusually porous and have small and abundant vesicles, and will float in water.

Scoria with larger vesicles and thick walls can also float if the vesicles are not interconnected. Fragments of floating scoria were observed at Taal Lake in 2023.[4] A priest who witnessed Taal Volcano's 1754 eruption noted in the lake a large quantity of floating rock which had been ejected by the volcano[5] and which later analysis found to be of basaltic composition.[6] Scoria from a 1993 undersea eruption near Socorro Island in the Pacific Ocean was observed to float on the ocean surface for up to 15 minutes before it sank.[7]

If the crust of a lava flow contains a large amount of vesicles, it is often called "scoria" or vesicular basalt. This form of scoria often has fewer vesicles and a higher specific gravity than the more typical scoria ejected as tephra. It is also formed as fragmental ejecta (lapilli, volcanic blocks, and volcanic bombs), for instance in Strombolian eruptions that form steep-sided scoria cones, also called cinder cones.[1]

Basaltic to andesitic Plinian eruptions can also form scoria like the basaltic 1085 eruption of Sunset Crater and the andesitic 2020 eruption of Taal. Scoria's holes or vesicles form when gases dissolved in the original 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. Most scoria is composed of glassy fragments and may contain phenocrysts. A sample from Yemen was mainly composed of volcanic glass with a few zeolites (e.g. clinoptilolite).[8]

The word scoria comes from Ancient Greek word σκωρία (skōría), meaning 'rust'. It is also the Italian term for slag. In earlier terminology, scoria was usually defined with a size range, e.g. 2–24 mm (0.079–0.945 in) in diameter, corresponding to lapilli, but neither color nor composition was typically a part of the definition.[9][10] During the 1980s, the size range disappeared from the definition, and a requirement was added that scoria be black or reddish in color and/or mafic to intermediate in composition.[1]

## Contents

* 1 Comparisons
* 2 Formation
* 3 Uses
* 4 See also
* 5 References
* 6 External links

## 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.[11]

## Formation

Pine trees growing on the slope of Cinder Cone, a volcanic cone of scoria in Lassen Volcanic National Park, California

As rising magma encounters lower pressures, dissolved gases are able to exsolve and form vesicles. Some of the vesicles are trapped when the magma chills and solidifies. Vesicles are usually small, spheroidal and do not impinge upon one another; instead, they open into one another with minimal distortion.

Volcanic cones of scoria can be left behind after eruptions, usually forming mountains with a crater at the summit. An example is Maungarei in Auckland, New Zealand, which like Te Tatua-a-Riukiuta in the south of the same city has been extensively quarried. Quincan, a unique variety of scoria, is quarried at Mount Quincan in Far North Queensland, Australia.

## Uses

Tuff moai with red scoria pukao on its head.

Scoria is used for a variety of purposes. It is commonly mined for use as loose construction aggregate in Europe, the Southwestern United States, Oregon[12] and Japan. Another major use of cinders is in manufacture of concrete and cinder blocks.

Scoria is also used in the construction of flexible, long-lasting roadbeds, due to its high strength and high angles of internal friction. Because of its good insulating properties, such roadbeds protect the ground beneath them from frost heave and heat deformation.[13] It is also spread as a traction aid on ice- and snow-covered roads, and around oil wells to firm up mud produced by heavy truck traffic.

Scoria is used in horticulture. Because it can hold water in its vesicles and in the pore space between grains in aggregates, it can improve the water-holding capacity of planting soils. When sorted to specific sizes and tightly packed, it is also an effective barrier against tunneling pests such as termites.[13] Its striking colours and water-holding properties can make it attractive for landscaping and drainage works.[14]

Scoria can be used for high-temperature insulation, as in gas barbecue grills.[15]

## See also

* Earth:Extrusive rock
* Earth:Igneous rock - Rock formed through the cooling and solidification of magma or lava
* Earth:List of rock types
* Earth:Tuff - Rock consolidated from volcanic ash

## References

1. ↑ 1.0 1.1 1.2 Fisher, R.V. and Schmincke, H.U., 1984. Pyroclastic rocks. Springer Science & Business Media. New York, New York, Springer Science & Business Media. 472 pp. ISBN 978-3-642-74864-6
2. ↑ 2.0 2.1 Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. 2005. p. 779. ISBN 0-922152-76-4.
3. ↑ McPhie, J., M. Doyle, and R. Allen (1993) Volcanic Textures A guide to the interpretation of textures in volcanic rocks Centre for Ore Deposit and Exploration Studies, University of Tasmania, Hobart, Tasmania. 198 pp. ISBN 9780859015226
4. ↑ Chavez, Pot (21 June 2023). “‘Floating’ rocks in Taal Lake not sign of volcanic eruption.” Philippine News Agency. Retrieved from https://www.pna.gov.ph/articles/1204022#:~:text=Rocks were found floating on lake water…
5. ↑ "Volcano Event Information – Event #754". National Centers for Environmental Information, NOAA. https://www.ngdc.noaa.gov/hazel/view/hazards/volcano/event-more-info/754. "Significant volcanic eruption event recorded in the NOAA NCEI Global Significant Volcanic EruptionsDatabase, with start date 15 May 1754, end date 4 December 1754, and a Volcanic Explosivity Index (VEI) of 4."
6. ↑ "Attention focuses on Taal: Decade volcano of the Philippines". Wiley on behalf of the American Geophysical Union. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/95EO00137. "Article discusses why Taal Volcano in the Philippines was selected as a Decade Volcano due to its complex eruptive history and significant hazard potential."
7. ↑ Siebe, C.; Komorowski, J.-C.; Navarro, C.; McHone, J.; Delgado, H.; Cortés, A. (1995). "Submarine eruption near Socorro Island, Mexico: Geochemistry and scanning electron microscopy studies of floating scoria and reticulite". Journal of Volcanology and Geothermal Research 68 (4): 239–271. doi:10.1016/0377-0273(95)00029-1.
8. ↑ Preliminary Assessment of Utilization of Al-Jaif Scoria (NW Sana'a, Yemen) for Cement Production
9. ↑ Stokes, W. L., and Varnes, D. J., 1955. Glossary of selected geologic terms, with special reference to their use in engineering: Denver. Proceedings of the Colorado Scientific Society. vol. 15, pp 1-165.
10. ↑ Wentworth, C.K. and Macdonald, G.A., 1953. Structures and forms of basaltic rocks in Hawaii. United States Geological Survey Bulletin. no. 944, pp 1-98.
11. ↑ Scoria from the Geology Science Website
12. ↑ Cascade Lakes Scenic Byway
13. ↑ 13.0 13.1 Dehn J., and McNutt, S.R., 2015. Volcanic materials in commerce and industry. In: Sigurdsson H., Houghton B., F., McNutt, S.R., Rymer, H., and Stix, J. (eds.) The encyclopedia of volcanoes. 2nd ed. England, Oxford, Elsevier. pp 1285-1294.
14. ↑ Three Kings Quarry , Winstone Aggregates.
15. ↑ Rock Types and Rocks Found in Michigan

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