Mineral
Alunite
KAl₃(SO₄)₂(OH)₆Alünit
The “alum stone” from which alum was made for centuries. Foça, Şaphane in Kütahya and Şebinkarahisar are Türkiye's old alum homelands.
Also known as: Alumstone
- Popularly: Ore and raw material
- Industrial
- Ore
- Important in Türkiye
In short
Alunite is a white, grey or reddish sulfate mineral of potassium, aluminium, sulfate and hydroxide (KAl₃(SO₄)₂(OH)₆). It forms when volcanic rocks are altered by hot, acid waters, and usually occurs as fine-grained masses intergrown with silica and clay. It does not dissolve in water, but once roasted and processed it yields alum, aluminium sulfate and potassium sulfate. That is why it has been mined as “alum stone” since the Middle Ages; Foça, Şaphane and Şebinkarahisar are among Türkiye's main alunite areas.
Photos
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How does it form?
Alunite forms when acid, sulfate-bearing waters act on aluminium-rich rocks. The Handbook of Mineralogy writes that it forms between 15 and 400 °C when sulfate, which may come from pyrite or volcanic vents, alters aluminous rocks, often together with kaolinisation and silicification. Kılınç Aksay and colleagues say alunite generally forms by hydrothermal (hot-water) alteration of volcanic rocks such as rhyolite, dacite and andesite, occurring in the rock as grains, pockets or veins; Wikipedia likewise describes it as veins and replacement masses in potassium-rich volcanic rocks such as trachyte and rhyolite.
The Şaphane deposit formed in rhyolitic tuffs and, in places, trachyte and trachyandesitic rocks; alongside the alunitisation there is silicification and clay formation (kaolinisation), and the silica and alunite are intergrown in a very fine-grained way (Kılınç Aksay et al.).
What is it used for?
- Alum: Alunite was mined for centuries to make alum. According to Tolun, in the old method alunite was first burned in heaps and left for a while; the pieces crumbled by themselves into a dark mud; the alum in the mud was dissolved by boiling it with water in copper kettles, poured off and left to crystallise. Alum was used as a mordant in dyeing cloth, in tanning leather and in water purification; according to Wikipedia, it is also used in barbers’ blocks as a styptic for shaving nicks.
- Aluminium sulfate: As the chemical industry developed, aluminium sulfate largely took the place of alum (Kılınç Aksay et al.; Wikipedia). Aluminium sulfate is used in water treatment, paper, textiles, leather, cement, ceramics, paint, the sugar industry, medicine and cosmetics, and in fire extinguishers.
- Potash fertiliser: Alunite is a valuable source of potassium sulfate (K₂SO₄). Potassium sulfate fertiliser is used mostly on potatoes, tobacco, vegetables, fruit, citrus, pulses, maize, cotton and sugar beet; according to Kılınç Aksay and colleagues, in the early 2000s all of Türkiye’s potassium fertilisers were imported. In the United States, potassium sulfate was made in wartime from the alunite of Marysvale, Utah (Tolun).
- Aluminium: Alunite is a possible source of alumina (USGS), but it has seldom been used because its cost cannot compete with bauxite. Tolun notes that Turkish alunite could, if need be, be used under special conditions to make aluminium too.
- Millstones: Silica-rich (quartz-bearing) alunite was also used in early times to make millstones.
In Türkiye
Türkiye has a long history of alunite and alum. According to Kılınç Aksay and colleagues, Türkiye’s largest known alunite deposits are in the Şebinkarahisar area of Giresun, the Şaphane area of Kütahya and the Foça area of İzmir; according to Turkish sources, alum was first made from alunite in the world in the 13th century around İzmir–Foça. The reserve figures below are old estimates made in the 1940s and do not show present workable reserves.
- Foça (İzmir): According to Wikipedia, the Genoese Zaccaria brothers obtained the alum mines of Foça in 1267 through a concession from Byzantium and ran the alum trade. According to Tolun (1950), good alunite lies near Foça on Şaphane Mountain and Kızıldağ; the iron oxide is generally below 0.5 percent, and about 1.35 million tons of reserves were estimated on Şaphane Mountain.
- Şaphane (Kütahya): The district’s name comes from şap (alum) and hane (works). According to Wikipedia, the alum mine, worked since Byzantine times, was an important trade commodity, Genoese merchants controlled alum extraction in the 13th–16th centuries, and in the Tanzimat period the Imperial Alum Administration (Şaphane-i Amire Müdürlüğü) answered directly to the sultan. Tolun estimated a reserve of about 1.44 million tons of alunite around the village. The ore sample Kılınç Aksay and colleagues studied holds about 66 percent silica, 22 percent aluminium oxide and 5.5 percent potassium oxide by weight. According to a local news report of 2026, the plant in the district made semi-finished aluminium sulfate, potassium aluminium sulfate and crystal alum (from the early 1970s to 2012); production stopped in 2012, and its reopening has been requested of the ministry.
- Şebinkarahisar (Giresun): According to Tolun, there is a large, rather scattered alunite deposit around the town; in 1947 he estimated about 30 million tons of visible reserves in the Gedehor area and found more than 70 percent alunite and less than 0.3 percent iron oxide in samples from two pits. He writes that this is one of the best alunites in the world. In the Küreze–Namuşar area the reserve is larger and the quality lower. According to Tolun’s 1950 article, these deposits were “waiting idle”.
Tolun wrote that Türkiye’s wealth in alunite is world-class and that alum and aluminium sulfate could always be obtained from it economically. Reserves and working may have changed in the seventy years since; the sources used on this page give no current national alunite reserve.
What determines its value?
Alunite is an industrial raw material bought and sold by the ton, and its value depends on its alunite content, how few impurities such as silica and iron oxide it carries, and the cost of processing. According to Tolun (1950), the Şebinkarahisar samples with more than 70 percent alunite and less than 0.3 percent iron oxide rank among the best-quality alunites in the world; in the Foça area, too, iron oxide is generally below 0.5 percent. Şaphane ore, by contrast, holds about 66 percent silica by weight and needs concentrating. To win alum, aluminium sulfate and potassium sulfate from the ore, calcining and leaching are needed, and it is hard to compete with aluminium sulfate made from bauxite (Tolun). The size of the deposit and the distance to the fertiliser and chemical industries matter too.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
A white, light grey, yellowish or reddish-brown, fine-grained, hard, porcelain-like mass; colourless when pure. Its rare crystals are small, glassy and pseudocubic or flat-hexagonal in shape (Handbook of Mineralogy).
- 2
Mohs hardness is 3.5–4 and density 2.6–2.9 g/cm³; the streak is white and it breaks with a shell-like (conchoidal) fracture.
- 3
It does not dissolve in water: according to Kılınç Aksay and colleagues, despite the sulfates in its structure alunite does not dissolve easily in water, but it does once calcined (its structure begins to break down above about 550 °C).
- 4
It usually lies in silicified and kaolinised (clay-altered) volcanic rocks; kaolinite, halloysite, diaspore, pyrite, gypsum and quartz may accompany it. Silica and alunite are often intergrown too finely to separate by eye, so a sure identification needs X-ray diffraction or a microscope.
Fakes and imitations
What shops usually don’t tell you:
- Alunite can look like kaolin (white clay), white chalcedony or chert, gypsum and quartz. Gypsum is scratched by a fingernail; kaolin is softer and crumbles in the hand.
- Jarosite, of the same group, looks much like it, but it holds iron instead of aluminium and is yellow-brown (see [jarosite](/en/stones/jarosite/)).
- The “alum stone” blocks sold at barbers and chemists are not alunite; they are usually potassium alum, which dissolves easily in water and tastes sweetish.
Safety
Alunite is harmless to handle. Its ore often holds a lot of silica (quartz); the fine dust raised in crushing and grinding should not be breathed, and a dust mask should be worn for dusty work. An ore sample from the Şaphane area, for example, contains about 66 percent silica by weight (Kılınç Aksay et al., 2004).
Myths and misconceptions
MythAlum and alunite are the same thing; an alum stone is simply alunite rock.
FactAlum is a double sulfate salt that dissolves easily in water and tastes sweetish (potassium alum, KAl(SO₄)₂·12H₂O). Alunite is a basic sulfate mineral from which alum can be made, and it does not dissolve in water; Tolun (1950) calls it a “basic alum”. To make alum, alunite is first roasted and then treated with hot water.
MythAluminium is made from alunite.
FactToday aluminium is made almost entirely from bauxite. Making alumina from alunite is technically possible, but Tolun (1950) writes that every method fails to compete with the Bayer process on cost; the USGS lists alunite only among possible additional sources of alumina (see [bauxite](/en/stones/bauxite/)).
Did you know?
Pure alunite contains about 37 percent aluminium oxide, 11.4 percent potassium oxide, 38.6 percent sulfur trioxide and 13 percent water by weight (Kılınç Aksay et al.).
Because it is quartz-bearing, alunite was also used in very early times to make millstones. According to Turkish sources, alunite was first used in the world for making alum in the 13th century around Foça.
At Tolfa in Italy large alunite deposits were found in 1461 and the Papal Treasury controlled the alum trade; Pope Pius II gave its distribution to the Medici, with the profits meant for Christian defence against Ottoman expansion (Wikipedia).
Alunite crystals are strongly pyroelectric: an electric charge appears on their faces as they are heated and cooled (Handbook of Mineralogy).
Where is it found?
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- Tolfa, Lazio, Italy · Historic sourceAccording to Wikipedia, alunite was first observed and mined for alum at Tolfa near Rome in the 15th century; Wikipedia says large alunite deposits were found there in 1461 and that the alum monopoly, under the control of the Papal Treasury, passed to the Medici and later to Agostino Chigi. The point is the position of the town of Tolfa.
- Marysvale area, Piute County, Utah, USA · Major depositThe Handbook of Mineralogy cites a very large alunite deposit near Marysvale (Ohio district). According to Tolun (1950), a plant to make potassium sulfate from alunite was built here in the United States in wartime. The point is the position of the town of Marysvale.
- Mukachevo and Berehove area, Zakarpattia, Ukraine · Historic sourceThe Handbook of Mineralogy lists Mukachevo (Muzijeva) and nearby Berehove among its alunite localities; Tolun (1950) mentions Beregszász in Hungary among smaller deposits of lower quality. The point is approximate, between the two towns.
- Rodalquilar, Almería, Spain · Known localityThe Spanish locality the Handbook of Mineralogy gives for alunite. The point is the position of the village of Rodalquilar.
- Rico district (Calico Peak), Dolores County, Colorado, USA · Known localityThe Handbook of Mineralogy puts about 100 million tons of alunite in the Calico Peak porphyry of the Rico district. The point is the position of the town of Rico.
- Bulahdelah, New South Wales, Australia · Known localityThe Handbook of Mineralogy and Wikipedia list Bulahdelah among the alunite localities. The point is the position of the town of Bulahdelah.
- Foça, İzmir, Türkiye · Historic sourceAccording to Turkish sources, alunite was first worked for alum in the world in the 13th century at İzmir–Foça. According to Wikipedia, the Genoese Zaccaria brothers obtained the alum mines of Phocaea in 1267 through a Byzantine concession. According to Tolun (1950), good alunite lies near Foça on Şaphane Mountain (estimated reserve about 1.35 million tons) and Kızıldağ. The point is the position of the town of Foça.
- Şaphane, Kütahya, Türkiye · Major depositIn the district, whose name comes from şap (alum) and hane (works), alunite has been worked since Byzantine times; in the Ottoman Tanzimat period there was an Imperial Alum Administration (Şaphane-i Amire Müdürlüğü) answering to the sultan (Wikipedia). The deposit is a zone of alunitised rhyolitic tuffs and trachytic-trachyandesitic rocks, with silicification and kaolinisation (Kılınç Aksay et al., 2004). Tolun (1950) estimated a reserve of about 1.44 million tons of alunite around the village. The point is the position of the town of Şaphane.
- Şebinkarahisar, Giresun, Türkiye · Major depositAccording to Tolun (1950), there is a large, rather scattered alunite deposit around Şebinkarahisar; in 1947 he estimated about 30 million tons of visible reserves in the Gedehor area and found more than 70 percent alunite and less than 0.3 percent iron oxide in samples from two pits. In the Küreze–Namuşar area the reserve is larger and the quality lower. The point is the position of the town of Şebinkarahisar. The figures are old estimates.
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is alunite?
Alunite is a white, grey or reddish sulfate mineral of potassium, aluminium, sulfate and hydroxide (KAl₃(SO₄)₂(OH)₆). It forms when volcanic rocks are altered by hot, acid waters, and usually occurs as fine-grained masses intergrown with silica and clay. It does not dissolve in water, but once roasted and processed it yields alum, aluminium sulfate and potassium sulfate. That is why it has been mined as “alum stone” since the Middle Ages; Foça, Şaphane and Şebinkarahisar are among Türkiye's main alunite areas.
What is alunite used for?
Alum: Alunite was mined for centuries to make alum. According to Tolun, in the old method alunite was first burned in heaps and left for a while; the pieces crumbled by themselves into a dark mud; the alum in the mud was dissolved by boiling it with water in copper kettles, poured off and left to crystallise. Alum was used as a mordant in dyeing cloth, in tanning leather and in water purification; according to Wikipedia, it is also used in barbers' blocks as a styptic for shaving nicks.
How hard is alunite?
It has a hardness of 3.5–4 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 2.6–2.9 g/cm³.
Where is alunite found?
Its best-known localities: Marysvale area, Piute County, Utah, USA; Şaphane, Kütahya, Türkiye; Şebinkarahisar, Giresun, Türkiye; Tolfa, Lazio, Italy; Mukachevo and Berehove area, Zakarpattia, Ukraine.
Where is alunite found in Türkiye?
Known localities in Türkiye: Şaphane, Kütahya, Türkiye; Şebinkarahisar, Giresun, Türkiye; Foça, İzmir, Türkiye.
How can you tell if alunite is real?
A white, light grey, yellowish or reddish-brown, fine-grained, hard, porcelain-like mass; colourless when pure. Its rare crystals are small, glassy and pseudocubic or flat-hexagonal in shape (Handbook of Mineralogy). Mohs hardness is 3.5–4 and density 2.6–2.9 g/cm³; the streak is white and it breaks with a shell-like (conchoidal) fracture. It does not dissolve in water: according to Kılınç Aksay and colleagues, despite the sulfates in its structure alunite does not dissolve easily in water, but it does once calcined (its structure begins to break down above about 550 °C). Alunite can look like kaolin (white clay), white chalcedony or chert, gypsum and quartz. Gypsum is scratched by a fingernail; kaolin is softer and crumbles in the hand.
Is alunite valuable?
On the “street to diamond” value ladder it sits on step 3 of nine: Building and industrial stone. Alunite is an industrial raw material bought and sold by the ton, and its value depends on its alunite content, how few impurities such as silica and iron oxide it carries, and the cost of processing. According to Tolun (1950), the Şebinkarahisar samples with more than 70 percent alunite and less than 0.3 percent iron oxide rank among the best-quality alunites in the world; in the Foça area, too, iron oxide is generally below 0.5 percent. Şaphane ore, by contrast, holds about 66 percent silica by weight and needs concentrating. To win alum, aluminium sulfate and potassium sulfate from the ore, calcining and leaching are needed, and it is hard to compete with aluminium sulfate made from bauxite (Tolun). The size of the deposit and the distance to the fertiliser and chemical industries matter too.
Is alunite dangerous?
Alunite is harmless to handle. Its ore often holds a lot of silica (quartz); the fine dust raised in crushing and grinding should not be breathed, and a dust mask should be worn for dusty work. An ore sample from the Şaphane area, for example, contains about 66 percent silica by weight (Kılınç Aksay et al., 2004).
Sources
- Alünitlerimizden İstifade İmkânları ve Şebinkarahisar Civarına Ait Numunelerle Yapılan Tecrübeler (R. Tolun), MTA Dergisi 40 · MTA Genel Müdürlüğü, 1950
- Türkiye Alunit Cevherinden Potasyum ve Alüminyum Sülfat Hammaddelerinin Kazanımı (E. Kılınç Aksay, A. Ünal, İ. Cöcen, E. Kaya, A. Akar), 5. Endüstriyel Hammaddeler Sempozyumu · Dokuz Eylül Üniversitesi, 2004
- Handbook of Mineralogy: Alunite · Mineralogical Society of America
- Şaphane · Vikipedi
- Şaphane · Wikipedia
- Şaphane'nin atıl şap madeni için yeniden üretim talebi · Yeni Birlik Gazetesi, 2026
- Foça · Wikipedia
- Tolfa · Wikipedia
- Alunite · Wikipedia
- Alum · Wikipedia
- Şap (bileşik) · Vikipedi
- Mineral Commodity Summaries 2026: Bauxite and Alumina · U.S. Geological Survey, 2026
External links
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On the same step
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