Rock
Scoria
Skorya (cüruf taşı)
Dark volcanic rock full of holes, frothed by gas and frozen in mid-air: the “cinder” used in gardens, barbecues and lightweight concrete.
Also known as: Cinder · Volcanic cinder
- Popularly: Ore and raw material
- Everyday
- Industrial
- Important in Türkiye
In short
Scoria is a dark, highly porous volcanic rock formed when gas-filled blobs of lava thrown out by a volcano cool in the air. Its composition is mostly basalt or andesite. It differs from pumice in being heavier, darker and in sinking in water in most pieces. It piles up around a vent to form scoria cones, and is abundant in young volcanic areas such as Kula. The “lava stone” bracelets sold in shops are usually made from scoria.
Photos
How does it form?
When pressure falls in rising magma, the gases in it (steam, carbon dioxide) separate into bubbles. Gas-rich lava thrown into the air in an explosion breaks into small pieces, and these freeze with their bubbles inside, turning into holey scoria. The pieces fall around the vent and pile up as steep-sided (30°-40° slope) scoria cones with a bowl-shaped crater. These cones are usually tens to a few hundred metres high.
Scoria is mostly basaltic or andesitic in composition. The reddish colours come from iron oxidising on contact with air. Lava richer in silica and more frothy forms pale pumice instead.
What is it used for?
- Lightweight concrete and building: Scoria (lava slag), tuff and pumice are among the natural lightweight aggregates, used in lightweight concrete and blocks.
- Road building: Used as fill in road foundations to protect against frost heave.
- Garden and landscaping: Used to aerate soil and help it hold water, and for drainage and decoration.
- Barbecues and heat: Used in gas barbecues as a high-temperature material that holds and spreads heat.
- Jewellery: Drilled and rounded scoria beads are sold as “lava stone”; for details see the lava stone page.
Scoria in Türkiye
The Kula-Salihli Geopark in Manisa has 80 scoria cones, none more than 150 metres high, and five maars (volcanic explosion craters) in an area of about 300 km². Three eruption phases took place about 1.1 million, 300,000 and 15,000 years ago. The ancient geographer Strabo called the region Katakekaumene, “the burnt land”. Kula’s jet-black lava flows and reddish scoria cones are among the best places to see scoria in nature. For pumice, see pumice.
What determines its value?
Scoria is a plentiful, cheap raw material sold by the bag or the tonne. Its value depends on grain size, pore structure, strength and transport cost: strong, evenly sized grains are wanted for lightweight concrete and road fill, while colourful, clean pieces are wanted for gardens and barbecues. A quarry near the surface and close to where it is used keeps costs low. For jewellery beads, workmanship (drilling, rounding) and evenness of size and colour matter; dyed beads are worth no more than natural-coloured ones.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
It is a dark brown, black, reddish brown or purplish red stone full of holes; the holes are large and round.
- 2
Its surface is rough and sharp-edged and feels like sandpaper in the hand. It is noticeably lighter than ordinary stone for its size, but not as light as pumice.
- 3
Most pieces sink when dropped in water; the light-coloured volcanic stone that floats is pumice.
- 4
When broken it is porous inside as well; the walls between the holes are glassy or fine-grained.
Fakes and imitations
What shops usually don’t tell you:
- “Slag” from iron and steel works (blast-furnace slag) is an artificial waste product that can be confused with natural scoria. Natural scoria occurs in volcanic regions.
- Most dark beads sold as “lava stone” in jewellery and ornaments are natural scoria or porous basalt; brightly coloured ones have been dyed.
- Volcanic tuff is porous too, but it is a clastic rock made of hardened ash; scoria is the lava fragments themselves.
Myths and misconceptions
MythCinder stone (“cüruf taşı”) is a factory waste product, an artificial material.
FactIn Turkish the word “cüruf” covers both the artificial waste of iron and steel works (blast-furnace slag) and natural volcanic scoria. Volcanic scoria (cinder) is entirely natural, formed when gas-frothed blobs of lava thrown from a volcano freeze.
MythScoria and pumice are the same stone.
FactBoth are porous, but pumice is pale, very light and usually floats, whereas scoria is dark, has larger holes and thicker walls between them, so most pieces sink.
Did you know?
In Mexico, Parícutin rose from the ground in a cornfield on 20 February 1943 and, in eruptions lasting until 1952, built a scoria cone 424 metres high.
In the Auckland volcanic field in New Zealand many scoria cones have been reduced, and some removed completely, because they were quarried for construction material.
Sunset Crater in Arizona takes its name from the reddish and orange scoria of the cone that formed around AD 1085.
Where is it found?
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- Sunset Crater, Arizona, USA · Known localityA scoria cone 340 metres high that formed around AD 1085; its reddish and orange scoria gave it its name. It was declared a national monument in 1930.
- Parícutin, Michoacán, Mexico · Historic sourceA volcano that appeared in a cornfield in 1943 and erupted until 1952, building a scoria cone 424 metres high.
- Cerro Negro, León, Nicaragua · Known localityA basaltic scoria cone 728 metres high whose name means “Black Hill”; it appeared in 1850 as the youngest volcano in Central America and has erupted about 23 times since.
- Auckland Volcanic Field, New Zealand · Known localityIn this field of about 53 volcanoes, the latest of which, Rangitoto, erupted about 600 years ago, many scoria cones have been reduced or removed by quarrying for construction material (especially scoria).
- Kula-Salihli Geopark, Manisa, Türkiye · Major depositIn an area of about 300 km² there are 80 scoria cones, none more than 150 metres high, and five maars; three eruption phases took place about 1.1 million, 300,000 and 15,000 years ago.
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is scoria?
Scoria is a dark, highly porous volcanic rock formed when gas-filled blobs of lava thrown out by a volcano cool in the air. Its composition is mostly basalt or andesite. It differs from pumice in being heavier, darker and in sinking in water in most pieces. It piles up around a vent to form scoria cones, and is abundant in young volcanic areas such as Kula. The “lava stone” bracelets sold in shops are usually made from scoria.
What is scoria used for?
Lightweight concrete and building: Scoria (lava slag), tuff and pumice are among the natural lightweight aggregates, used in lightweight concrete and blocks. Road building: Used as fill in road foundations to protect against frost heave. Garden and landscaping: Used to aerate soil and help it hold water, and for drainage and decoration. Barbecues and heat: Used in gas barbecues as a high-temperature material that holds and spreads heat. Jewellery: Drilled and rounded scoria beads are sold as “lava stone”; for details see the lava stone page.
How hard is scoria?
It has a hardness of 5–6 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 1–2 g/cm³.
Where is scoria found?
Its best-known localities: Kula-Salihli Geopark, Manisa, Türkiye; Parícutin, Michoacán, Mexico; Sunset Crater, Arizona, USA; Cerro Negro, León, Nicaragua; Auckland Volcanic Field, New Zealand.
Where is scoria found in Türkiye?
Known localities in Türkiye: Kula-Salihli Geopark, Manisa, Türkiye.
How can you tell if scoria is real?
It is a dark brown, black, reddish brown or purplish red stone full of holes; the holes are large and round. Its surface is rough and sharp-edged and feels like sandpaper in the hand. It is noticeably lighter than ordinary stone for its size, but not as light as pumice. Most pieces sink when dropped in water; the light-coloured volcanic stone that floats is pumice. “Slag” from iron and steel works (blast-furnace slag) is an artificial waste product that can be confused with natural scoria. Natural scoria occurs in volcanic regions.
Is scoria valuable?
On the “street to diamond” value ladder it sits on step 2 of nine: Raw material by the tonne. Scoria is a plentiful, cheap raw material sold by the bag or the tonne. Its value depends on grain size, pore structure, strength and transport cost: strong, evenly sized grains are wanted for lightweight concrete and road fill, while colourful, clean pieces are wanted for gardens and barbecues. A quarry near the surface and close to where it is used keeps costs low. For jewellery beads, workmanship (drilling, rounding) and evenness of size and colour matter; dyed beads are worth no more than natural-coloured ones.
Sources
- Scoria · Wikipedia
- Skorya · Vikipedi
- Cinder cone · Wikipedia
- Sunset Crater · Wikipedia
- Parícutin · Wikipedia
- Cerro Negro · Wikipedia
- Auckland volcanic field · Wikipedia
- Kula Volcanic Geopark · Wikipedia
- Scoria: a natural lightweight aggregate (Patty), Texas Highway Department · Texas Archive, University of Texas, 1971
- Hafif beton (Kabay & Aköz), Beton 2023 Kongresi Çağrılı Bildirileri · Türkiye Hazır Beton Birliği, 2023
External links
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On the same step
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A green amphibole that grows like rays: a raw material of nephrite jade and cat's-eye stones; its fibrous form is asbestos.
Amphibolite
A dark, heavy, salt-and-pepper metamorphic rock: basalt or gabbro transformed at depth; the stone of Neolithic axes.
Andesite
The rock of volcanic arcs, named after the Andes — and the pink-grey stone of Ankara Castle.