Alum-(K)
A valid IMA mineral species - grandfathered
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About Alum-(K)
Formula:
KAl(SO4)2 · 12H2O
Colour:
Colourless, white; colourless in transmitted light.
Lustre:
Vitreous
Hardness:
2
Specific Gravity:
1.757
Crystal System:
Isometric
Member of:
Name:
The name is derived from "alum" since this species is a member of the alum group; the -(K) suffix denotes that it is the K-dominant member of the group. Renamed from potassium alum to alum-(K) in 2008.
Unique Identifiers
Mindat ID:
3267
Long-form identifier:
mindat:1:1:3267:0
Similar Names
| Alm | A synonym of 'Chalk' | |
| Alum-(Na) | A valid IMA mineral species - grandfathered | NaAl(SO4)2 · 12H2O |
| Alun | A synonym of Alum Group | |
| K-alum | ||
| Ólom | A synonym of Native Lead |
IMA Classification of Alum-(K)
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
KAl(S6+O4)2·12H2O
Classification of Alum-(K)
7.CC.20
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
C : With medium-sized and large cations
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
C : With medium-sized and large cations
29.5.5.1
29 : HYDRATED ACID AND NORMAL SULFATES
5 : AB(XO4)2·xH2O
29 : HYDRATED ACID AND NORMAL SULFATES
5 : AB(XO4)2·xH2O
25.6.17
25 : Sulphates
6 : Sulphates of Al and Tl
25 : Sulphates
6 : Sulphates of Al and Tl
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Aum-K | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Alum-(K)
Vitreous
Transparency:
Transparent
Colour:
Colourless, white; colourless in transmitted light.
Hardness:
2 on Mohs scale
Cleavage:
Poor/Indistinct
{111}, traces.
{111}, traces.
Fracture:
Conchoidal
Density:
1.757 g/cm3 (Measured) 1.753 g/cm3 (Calculated)
Optical Data of Alum-(K)
Type:
Isotropic
Chemistry of Alum-(K)
Mindat Formula:
KAl(SO4)2 · 12H2O
Element Weights:
Crystallography of Alum-(K)
Crystal System:
Isometric
Class (H-M):
m3(2/m3) - Diploidal
Space Group:
Pa3
Cell Parameters:
a = 12.157(3) Å
Unit Cell V:
1,796.72 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Crystals octahedral if precipitated from pure water solution; cubic from alkaline solutions. Commonly massive with a columnar or granular structure; stalactitic, mealy coatings.
Twinning:
On {111}, very rare.
Crystallographic forms of Alum-(K)
Crystal Atlas:
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Potassiumalum no.3 - {100} - Goldschmidt (1913-1926)
Potassiumalum no.27 - {111} - Goldschmidt (1913-1926)
Potassiumalum no.28 - {111} - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by
www.smorf.nl.
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0009912 | Alum-(K) | Nyburg S C, Steed J, Aleksovska S, Petrusevski V M (2000) Structure of the alums. I. On the sulfate group disorder in the alpha-alums Acta Crystallographica B56 204-209 |  | 2000 | synthetic | 0 | 293 |
| 0009911 | Alum-(K) | Nyburg S C, Steed J, Aleksovska S, Petrusevski V M (2000) Structure of the alums. I. On the sulfate group disorder in the alpha-alums Acta Crystallographica B56 204-209 | | 2000 | synthetic | 0 | 293 |
| 0019046 | Alum-(K) | Larson A C, Cromer D T (1967) Refinement of the alum structures. III. X-ray study of the a alums, K, Rb and NH4Al(SO4)2*12H2O Acta Crystallographica 22 793-800 | | 1967 | Synthetic | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Loading XRD data...
Data courtesy of RRUFF project at University of Arizona, used with permission.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 45a : [Sulfates, arsenates, selenates, antimonates] | |
| 47a : [Near-surface hydration of prior minerals] | |
| 47b : [Sulfates and sulfites] | |
| Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere | <0.6 |
| 50 : Coal and/or oil shale minerals | <0.36 |
Type Occurrence of Alum-(K)
Synonyms of Alum-(K)
Other Language Names for Alum-(K)
French:Alum-(K)
German:Kalialaun
Kalialaun (in part)
Kalinischer Alumsulphat (in part)
Kalialaun (in part)
Kalinischer Alumsulphat (in part)
Norwegian:Alum-(K)
Russian:Алюмокалиевые квасцы
Varieties of Alum-(K)
| Thallium-bearing Alum-(K) | Empirical formula (Fornovolasco material): (K0.74Tl0.10)Σ0.84(Al0.84Fe0.14)Σ0.98S2.03O8·12H2O. |
Relationship of Alum-(K) to other Species
Member of:
Other Members of Alum Group:
| Alum-(Na) | NaAl(SO4)2 · 12H2O | Iso. m3(2/m3) : Pa3 |
| Lanmuchangite | Tl+Al(SO4)2 · 12H2O | Iso. m3(2/m3) : Pa3 |
| Tschermigite | (NH4)Al(SO4)2 · 12H2O | Iso. m3(2/m3) : Pa3 |
Common Associates
Associations Based on Photo Data:
| 6 photos of Alum-(K) associated with Native Sulphur | S8 |
| 3 photos of Alum-(K) associated with Halotrichite | Fe2+Al2(SO4)4 · 22H2O |
| 2 photos of Alum-(K) associated with Magnanelliite | K3Fe3+2(SO4)4(OH)(H2O)2 |
| 2 photos of Alum-(K) associated with Krausite | KFe(SO4)2 · H2O |
| 2 photos of Alum-(K) associated with Pickeringite | MgAl2(SO4)4 · 22H2O |
| 1 photo of Alum-(K) associated with Guérinite | Ca6(HAsO4)3(AsO4)2 · 10.5H2O |
| 1 photo of Alum-(K) associated with Pyrite | FeS2 |
| 1 photo of Alum-(K) associated with Giacovazzoite | K5Fe3+3O(SO4)6 · 10H2O |
| 1 photo of Alum-(K) associated with Hexahydrite | Mg(H2O)6(SO4) |
| 1 photo of Alum-(K) associated with Copiapite Group |
Related Minerals - Strunz-mindat Grouping
| 7.CC. | Cobaltoblödite | Na2Co(SO4)2 · 4H2O |
| 7.CC. | Andychristyite | PbCu2+Te6+O5(H2O) |
| 7.CC. | Ammoniovoltaite | (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18 |
| 7.CC.05 | Krausite | KFe(SO4)2 · H2O |
| 7.CC.10 | Tamarugite | NaAl(SO4)2 · 6H2O |
| 7.CC.15 | Mendozite | NaAl(SO4)2 · 11H2O |
| 7.CC.15 | Kalinite | KAl(SO4)2 · 11H2O |
| 7.CC.20 | Alum-(Na) | NaAl(SO4)2 · 12H2O |
| 7.CC.20 | Lonecreekite | (NH4)Fe3+(SO4)2 · 12H2O |
| 7.CC.20 | Tschermigite | (NH4)Al(SO4)2 · 12H2O |
| 7.CC.20 | Lanmuchangite | Tl+Al(SO4)2 · 12H2O |
| 7.CC.25 | Zincovoltaite | K2Zn5Fe3+3Al(SO4)12 · 18H2O |
| 7.CC.25 | Voltaite | K2Fe2+5Fe3+3Al(SO4)12 · 18H2O |
| 7.CC.25 | Magnesiovoltaite | K2Mg5Fe3+3Al(SO4)12 · 18H2O |
| 7.CC.25 | Pertlikite | K2(Fe2+,Mg)2(Mg,Fe3+)4Fe3+2Al(SO4)12 · 18H2O |
| 7.CC.25 | Ammoniomagnesiovoltaite | (NH4)2Mg2+5Fe3+3Al(SO4)12 · 18H2O |
| 7.CC.30 | Kröhnkite | Na2Cu(SO4)2 · 2H2O |
| 7.CC.35 | Ferrinatrite | Na3Fe(SO4)3 · 3H2O |
| 7.CC.40 | Goldichite | KFe(SO4)2 · 4H2O |
| 7.CC.45 | Löweite | Na12Mg7(SO4)13 · 15H2O |
| 7.CC.50 | Nickelblödite | Na2Ni(SO4)2 · 4H2O |
| 7.CC.50 | Blödite | Na2Mg(SO4)2 · 4H2O |
| 7.CC.50 | Changoite | Na2Zn(SO4)2 · 4H2O |
| 7.CC.55 | Leonite | K2Mg(SO4)2 · 4H2O |
| 7.CC.55 | Mereiterite | K2Fe(SO4)2 · 4H2O |
| 7.CC.60 | Nickelpicromerite | K2Ni(SO4)2 · 6H2O |
| 7.CC.60 | Nickelboussingaultite | (NH4)2Ni(SO4)2 · 6H2O |
| 7.CC.60 | Katerinopoulosite | (NH4)2Zn(SO4)2 · 6H2O |
| 7.CC.60 | Picromerite | K2Mg(SO4)2 · 6H2O |
| 7.CC.60 | Cyanochroite | K2Cu(SO4)2 · 6H2O |
| 7.CC.60 | Mohrite | (NH4)2Fe(SO4)2 · 6H2O |
| 7.CC.60 | Boussingaultite | (NH4)2Mg(SO4)2 · 6H2O |
| 7.CC.65 | Polyhalite | K2Ca2Mg(SO4)4 · 2H2O |
| 7.CC.70 | Leightonite | K2Ca2Cu(SO4)4 · 2H2O |
| 7.CC.75 | Amarillite | NaFe(SO4)2 · 6H2O |
| 7.CC.80 | Konyaite | Na2Mg(SO4)2 · 5H2O |
| 7.CC.85 | Wattevilleite | Na2Ca(SO4)2 · 4H2O (?) |
| 7.CC.85 | Xocolatlite | Ca2Mn4+2(Te6+O6)2 · H2O |
| 7.CC.90 | Eckhardite | (Ca,Pb)Cu2+Te6+O5(H2O) |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 8.2418% | 2,555 | β, γ |
For comparison:
- Banana: ~15 Bq per fruit
- Granite: 1,000–3,000 Bq/kg
- EU exemption limit: 10,000 Bq/kg
Note: Risk is shown relative to daily recommended maximum exposure to non-background radiation of 1000 µSv/year. Note that natural background radiation averages around 2400 µSv/year so in reality these risks are probably extremely overstated! With infrequent handling and safe storage natural radioactive minerals do not usually pose much risk.
Interactive Simulator:
Note: The mass selector refers to the mass of radioactive mineral present, not the full specimen, also be aware that the matrix may also be radioactive, possibly more radioactive than this mineral!
Activity: –
| Distance | Dose rate | Risk |
|---|---|---|
| 1 cm | ||
| 10 cm | ||
| 1 m |
The external dose rate (D) from a radioactive mineral is estimated by summing the gamma radiation contributions from its Uranium, Thorium, and Potassium content, disregarding daughter-product which may have a significant effect in some cases (eg 'pitchblende'). This involves multiplying the activity (A, in Bq) of each element by its specific gamma ray constant (Γ), which accounts for its unique gamma emissions. The total unshielded dose at 1 cm is then scaled by the square of the distance (r, in cm) and multiplied by a shielding factor (μshield). This calculation provides a 'worst-case' or 'maximum risk' estimate because it assumes the sample is a point source and entirely neglects any self-shielding where radiation is absorbed within the mineral itself, meaning actual doses will typically be lower. The resulting dose rate (D) is expressed in microsieverts per hour (μSv/h).
D = ((AU × ΓU) + (ATh × ΓTh) + (AK × ΓK)) / r2 × μshield
Other Information
Thermal Behaviour:
Rapid heating to below red heat, it intumesces and forms a bulky, porous mass of the anhydrous sulfate ("burnt alum").
Notes:
Soluble in water. Melts in its water of crystallization at 91 deg.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Alum-(K)
mindat.org URL:
https://www.mindat.org/min-3267.html
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References for Alum-(K)
Reference List:
Spangenberg (1925) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 61: 189.
Larson, A. C., Cromer, D. T. (1967) Refinement of the alum structures. III. X-ray study of the α alums, K, Rb and NH4Al(SO4)2.12H2O. Acta Crystallographica, 22 (6) 793-800 doi:10.1107/s0365110x67001586
Eysel, Hans Hermann; Eckert, J. (1976) Einkristall‐Raman‐Spektren von Alaunen. I. Innere Schwingungen, Frequenzbereich 300 bis 1200 cm−1. Zeitschrift für anorganische und allgemeine Chemie, 424 (1). 68-80 doi:10.1002/zaac.19764240111
Eckert, J.; Eysel, H. H.; Kampffmeyer, G. L. (1976) Einkristall‐Raman‐Spektren von Alaunen. II. [1]. Raman‐aktive Gitterschwingungen und FIR‐Spektren. Zeitschrift für anorganische und allgemeine Chemie, 424 (1). 81-86 doi:10.1002/zaac.19764240112
Localities for Alum-(K)
Showing 129 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Argentina | |
| Saravia (1960) |
| Bengochea +1 other reference |
Austria | |
| Strasser (1989) |
| - (1994, July) |
Bolivia | |
| [www.hedegaard.com] +1 other reference |
| Salomon Rivas & Federico Ahlfeld (1998) |
Chile | |
| Chukanov et al. (2016) |
| Palache et al. (1951) |
| Aguilera et al. (2016) | |
China | |
| Chen Daiyan et al. (2001) |
| Wen et al. (2020) +1 other reference |
| Liu et al. (2024) |
Czech Republic | |
| Breiter K. (1976) |
| Breiter K. (1976) | |
| Breiter K. (1976) |
| Breiter K. (1976) |
| Breiter K. (1976) |
| Hršelová et al. (2013) |
Germany | |
| Walenta (1992) |
| Aufschluss 1984 (1) |
| Mineralogical Society of America - ... |
| Weiß (1990) |
| Schnorrer-Köhler (1986) +2 other references |
| Blass et al. (1996) +1 other reference |
| Košek (2018) | |
| Frenzel (1964) |
| Schneider (1991) |
| Mineralogical Society of America - ... |
| EDX and XRD confirmed by Dr. Th. Witzke |
| Witzke et al. (1998) |
| Mineralogical Society of America - ... |
Greece | |
| Daniel Hummer Collection |
| Rieck (n.d.) |
Hungary | |
| GEODA 2007/1 |
| Lovász & Szabó (2014) |
| Own collecting and analysed (2005) |
| Geoda | |
Iran | |
| Bariand et al. (1977) |
Ireland | |
| Alfredo Petrov specimen (obtained from Dr Marco Marcchesini) |
Italy | |
| Mineralogical Society of America - ... |
| Scacchi A. (1849) +1 other reference |
| Russo et al. (2004) |
| Russo +1 other reference | |
| Russo et al. (2017) |
| Mormone et al. (2015, April) +1 other reference | |
| Russo et al. (2017) |
| Russo et al. (2004) +1 other reference |
| Pelloux (1927) +3 other references | |
| Pellino et al. (2025) | |
| Del Caldo et al. (1973) +1 other reference |
| Fernando Caboni et al. (2024) |
| Fernando Caboni et al. (2024) | |
| D'Angeli et al. (2018) |
| Brescia et al. (2025) |
| Russo (2006) |
| Russo (2006) |
| Cossa (1881) +3 other references |
| Cossa (1881) +3 other references |
| Panichi (1914) +2 other references |
| COSSA A. (1881) | |
| Campostrini et al. (2011) | |
| Bazzoni et al. (2015) |
| [var: Thallium-bearing Alum-(K)] Biagioni et al. (2011) +1 other reference |
| Mauro D. (2016) +1 other reference | |
| Biagioni et al. (2019) +1 other reference |
| 9 (2) +3 other references |
Japan | |
| Ibaraki et al. (1991) |
| Ibaraki et al. (1991) | |
| Petrov (n.d.) +1 other reference |
Mexico | |
| Wilson W.E. (2024) |
Norway | |
| L. Kruszewski specimen |
Pakistan | |
| M. Qasim Jan et al. (1985) |
Poland | |
| Marszałek +2 other references |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Ciesielczuk et al. (2014) |
| Berg G. 1935: Erläuterungen zu Blatt ... |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Lis et al. (1986) |
| Kruszewski (2012) |
Portugal | |
| Flahaut et al. (2018, September) |
| Luigi Chiappino collection | |
Romania | |
| Łukasz Kruszewski PXRD & pXRF analysis ... |
Russia | |
| Okrugin (2004) |
South Africa | |
| Martini (1997) |
South Korea | |
| Rutgers College Geological Museum ... |
Spain | |
| Mingueza et al. (Min. Catalunya/Paragénesis, 2025) |
Switzerland | |
| Erik Vercammen collection |
UK | |
| Ford et al. (1993) |
| Hall (1868) |
| Palache et al. (1951) |
| Livingstone et al. (1983) |
USA | |
| Anatoly Kasatkin analyses |
| Hanson et al. (2008) |
| Palache et al. (1951) +1 other reference |
| Adams et al. (2014) |
| Dana 7: I: 143 +2 other references |
| California State University (2000) +1 other reference |
| Weber (1963) +3 other references |
| Mineralogical Society of America - ... |
| Eckel et al. (1997) |
| Eckel et al. (1997) |
| Erd et al. (1960) |
| Erd et al. (1960) |
| Erd et al. (1960) |
| Erd et al. (1960) | |
| Erd et al. (1960) |
| Uwe Kolitsch (SXRD analysis) +3 other references |
| Mineralogical Society of America - ... | |
| Carlson (2015) |
| Carlson (2015) |
| Carlson (2015) |
| Montgomery (Jan, 1963) +2 other references |
| Lapham et al. (1980) |
| Downey et al. (1974) +1 other reference |
| Bernard et al. (2004) |
| Plášil et al. (2023) |
| Bullock (1981) |
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Lichtenberg Absetzer dump, Kauern, Greiz District, Thuringia, Germany