![Scoria Macro Digon3](https://upload.wikimedia.org/wikipedia/commons/1/18/Scoria_Macro_Digon3.jpg)
Scoria is a
pyroclastic
Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
, highly
vesicular, dark-colored
volcanic rock
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...
that was ejected from a
volcano
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates are ...
as a molten blob and cooled in the air to form discrete grains or
clast
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
s.
[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 (generally dark brown, black or purplish-red), and
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic or
andesitic
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...
in composition. Scoria is relatively low in
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
, all scoria has a
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
greater than 1, and sinks in water.
The holes or vesicles form when gases that were dissolved in the
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
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. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (
lapilli
Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones".
By definition lapilli range f ...
, blocks and bombs), for instance in
Strombolian eruptions that form steep-sided
scoria cone
Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''G ...
s. Most scoria is composed of glassy fragments and may contain
phenocrysts
300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...
. Analysis of scoria found in
Yemen
Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...
showed that it was mainly composed of
volcanic glass
Volcanic glass is the amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the closely packed, highly ordered array of a crystal and the highly disordered array of liqu ...
with a few
zeolites
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These pos ...
(e.g.
clinoptilolite
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula . It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to ...
). The word ''scoria'' comes from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
σκωρία, ''skōria'', rust. The term cinder is now considered to be synonomous and interchangeable with the term ''scoria'', and ''scoria'' is the preferred term used in the 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. ]
Eruption of scoria frequently form volcanic cones, called either
cinder cone
A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions o ...
s or scoria cones.
Prior to the 1980s, neither color nor composition was typically a part of the definition and a size range of the particles, e.g. in diameter, was usually specified.
[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 that scoria be black or reddish in color, mafic in composition, or combination of both was added.
[Fisher, R.V. and Schmincke, H.U., 1984. ''Pyroclastic rocks.'' Springer Science & Business Media. New York, New York, Springer Science & Business Media. 472 pp. ]
Comparisons
Scoria differs from
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
, 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
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 little distortion.
Volcanic cone
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and ...
s of scoria can be left behind after eruptions, usually forming mountains with a crater at the summit. An example is
Maungarei
Maungarei (officially known as Maungarei / Mount Wellington) is a 135-metre volcanic peak and Tūpuna Maunga (ancestral mountain) located in the Auckland volcanic field of Auckland, New Zealand. It is the youngest onshore volcano of the Auckl ...
in
Auckland
Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...
,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, which like
Te Tatua-a-Riukiuta in the south of the same city has been extensively quarried. Quincan, a unique form of Scoria, is quarried at
Mount Quincan
Mount Quincan is a volcanic mountain near Yungaburra on the Atherton Tableland in Far North Queensland, Australia.
The extinct volcano is one of many cinder cones in the Atherton Tableland region. Its crater is approximately 500 m across, wit ...
in
Far North Queensland
Far North Queensland (FNQ) is the northernmost part of the Australian state of Queensland. Its largest city is Cairns and it is dominated geographically by Cape York Peninsula, which stretches north to the Torres Strait, and west to the Gulf C ...
,
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
.
Uses
![Ahu Tahai](https://upload.wikimedia.org/wikipedia/commons/c/c8/Ahu_Tahai.jpg)
Scoria has several useful characteristics that influence how it is used. It is somewhat porous, has a high surface area and strength for its weight, and often has striking colours. Consequently, it is often used in landscaping and drainage works. It is also commonly used in gas barbecue grills.
Rock Types and Rocks Found in Michigan
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Scoria can be used for high-temperature insulation. It is also used on oil well sites to limit mud problems resulting from heavy truck traffic.
The quarry of Puna Pau
Maunga Puna Pau is a small crater or cinder cone and prehistoric quarry on the outskirts of Hanga Roa in the south west of Easter Island (a Chilean island in the Pacific Ocean). Puna Pau gives its name to one of the seven regions of the Rapa Nui ...
on Rapa Nui
Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearly ...
/Easter Island
Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearl ...
was the source of a red-coloured scoria which the Rapanui
The Rapa Nui (Rapa Nui: , Spanish: ) are the Polynesian peoples indigenous to Easter Island. The easternmost Polynesian culture, the descendants of the original people of Easter Island make up about 60% of the current Easter Island population and ...
people used to carve the pukao
Pukao are the hat-like structures or topknots formerly placed on top of some moai statues on Easter Island. They were all carved from a very light-red volcanic scoria, which was quarried from a single source at Puna Pau.
Symbolism
Pukao were not ...
(or topknots) for their distinctive moai
Moai or moʻai ( ; es, moái; rap, moʻai, , statue) are monolithic human figures carved by the Rapa Nui people on Easter Island, Rapa Nui in eastern Polynesia between the years 1250 and 1500. Nearly half are still at Rano Raraku, the main mo ...
statues, and even to carve some moai themselves.
It is also used as a traction aid on ice- and snow-covered roads.
Scoria is mined and used for a variety of purposes. It commonly mined for use as loose construction aggregate
Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates ...
in Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, the Southwestern United States
The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, Ne ...
, and Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. Another major use of cinders is in manufacture of concrete and cinder block
A concrete masonry unit (CMU) is a standard-size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
Tho ...
s. In fact, the widespread use of cinders as construction aggregates by ancient Romans
In modern historiography, ancient Rome refers to Roman people, Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom ...
was one of earliest industrial uses of volcanic rocks.[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.]
Because of its high strength, high angles of internal friction, and with good insulating properties, scoria is also used in the construction of flexible, long-lasting roadbed
A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation.
There are many types of ...
s. Because of insulating properties of scoria, such roadbeds protect the ground beneath them from extreme temperatures, and the associated deformation. Also, it can be used to minimize the effect of annual frost heave
Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated int ...
and permafrost
Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...
on roads.
Scoria has horticultural uses. Because it can hold water in its vesicles and in the pore space between grains in aggregates, it is used to improve the capacity of soils surrounding plants to hold moisture. When sorted to specific sizes, it is also an effective barrier for tunneling pests, such as termites. Its ragged surfaces allow it to be tightly packed and interlocked enough such that termites and other pests cannot fit between individual particles.
See also
*
*
*Igneous rock
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock ...
*
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References
External links
*{{commons-inline
Volcanic rocks
Glass in nature
Igneous petrology
Tephra