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Scoria or cinder is a Pyroclastic rock, 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 .Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. It is typically dark in color (brown, black or purplish-red), and or andesite in composition. Scoria has relatively low density, as it is riddled with macroscopic ellipsoidal vesicles (gas bubbles), but in contrast to pumice, scoria always has a specific gravity greater than 1 and sinks in water.
Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (lapilli, blocks, and bombs), for instance in Strombolian eruptions that form steep-sided cinder cone, also called . 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). Preliminary Assessment of Utilization of Al-Jaif Scoria (NW Sana'a, Yemen) for Cement Production
The Geology term cinder is synonymous and interchangeable with scoria, though scoria is preferred in scientific literature.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. The word comes from Greek language σκωρία, skōria, rust. In earlier terminology, scoria was usually defined with a size range, e.g. in diameter, but neither color nor composition was typically a part of the definition.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.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. 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 in composition.Fisher, R.V. and Schmincke, H.U., 1984. Pyroclastic rocks. Springer Science & Business Media. New York, New York, Springer Science & Business Media. 472 pp.
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.
Scoria is also used in the construction of flexible, long-lasting , 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.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. 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. Its striking colours and water-holding properties can make it attractive for landscaping and drainage works. Three Kings Quarry, Winstone Aggregates.
Scoria can be used for high-temperature insulation, as in gas barbecue grills. Rock Types and Rocks Found in Michigan
The Roman people used cinders as construction aggregates, one of the earliest industrial uses of volcanic rocks. On Rapa Nui/Easter Island, the quarry of Puna Pau was the source of reddish scoria used to carve the pukao (topknots) for the famous moai statues, and even for the main bodies of some moai.
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