View source for Scoria

{{short description|Dark vesicular volcanic rock}}
{{other uses}}
{{Refimprove|date=September 2010}}

[[File:Scoria Macro Digon3.jpg|thumb|Scoria]]
'''Scoria''' or '''cinder''' is a [[Pyroclastic rock|pyroclastic]], highly [[Vesicular texture|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 [[clast]]s.<ref name="FisherOthers1984a"/><ref name="NeuendorfOthers2005a">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. {{ISBN|0-922152-76-4}}</ref> It is typically dark in color (brown, black or purplish-red), and [[basalt]]ic or [[andesite|andesitic]] 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 eruption]]s that form steep-sided [[cinder cone|scoria cone]]s, also called [[cinder cone]]s.<ref name="FisherOthers1984a" /> 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]]).<ref>[https://www.researchgate.net/publication/330007091_Preliminary_Assessment_of_Utilization_of_Al-Jaif_Scoria_NW_Sana'a_Yemen_for_Cement_Production Preliminary Assessment of Utilization of Al-Jaif Scoria (NW Sana'a, Yemen) for Cement Production]</ref>  

The [[Geology|geological]] term '''cinder''' is synonymous and interchangeable with ''scoria'', though ''scoria'' is preferred in scientific literature.<ref name="NeuendorfOthers2005a" /><ref name="McPhieOthers1993a">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}}</ref> The word comes from [[Greek language|Greek]] σκωρία, ''skōria'', rust. In earlier terminology, scoria was usually defined with a size range, e.g. {{convert|2 to 24|mm|in|abbr=on}} in diameter, but neither color nor composition was typically a part of the definition.<ref name="StokeOthers1955a">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.</ref><ref name="Wentworth1953a">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.</ref> 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.<ref name="FisherOthers1984a">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}}</ref>

==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.

==Formation==
[[File:Pine trees growing on the slope of Cinder Cone.jpg|thumb|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 [[wikt:exsolve|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 cone]]s 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==
[[File:Ahu Tahai.jpg|thumb|upright|[[Tuff]] [[moai]] with red scoria [[pukao]] on its head.|150px]]Scoria is used for a variety of purposes. It is commonly mined for use as loose [[construction aggregate]] in [[Europe]], the [[Southwestern United States]], and [[Japan]]. Another major use of cinders is in manufacture of concrete and [[cinder block]]s. 

Scoria is also used in the construction of flexible, long-lasting [[roadbed]]s, 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.<ref name="DehnOthers2015a">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.</ref> 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.<ref name="DehnOthers2015a" /> Its striking colours and water-holding properties can make it attractive for landscaping and drainage works.<ref>[http://www.winstoneaggregates.co.nz/Auckland.php?location=Three%20Kings Three Kings Quarry] {{Webarchive|url=https://web.archive.org/web/20110724195217/http://www.winstoneaggregates.co.nz/Auckland.php?location=Three%20Kings |date=2011-07-24 }}, Winstone Aggregates.</ref> 

Scoria can be used for high-temperature insulation, as in gas barbecue grills.<ref>[http://www.michigan.gov/documents/deq/GIMDL-GGRF_307777_7.pdf Rock Types and Rocks Found in Michigan]</ref>

The [[Roman people|ancient Romans]] used cinders as construction aggregates, one of the earliest industrial uses of volcanic rocks.<ref name="DehnOthers2015a" /> 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]].

==See also==
*{{annotated link|Cinder track}}
*{{annotated link|Extrusive rock}}
*[[Igneous rock]]
*{{annotated link|Lapilli}}
*{{annotated link|List of rock types}}
*{{annotated link|Parícutin}}
*{{annotated link|Tephra}}
*{{annotated link|Tuff}}
*{{annotated link|Volcano}}
*{{annotated link|Volcanic bomb}}
*{{annotated link|Ye Olde Cinder House}}
*{{Annotated link|Pumice}}
*[[Cinder cone]]

==References==
{{Reflist}}

==External links==
*{{commons-inline}}
{{Volcanoes}}
{{Rock type}}
[[Category:Volcanic rocks]]
[[Category:Glass in nature]]
[[Category:Igneous petrology]]
[[Category:Tephra]]