Picromerite
A valid IMA mineral species - grandfathered
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About Picromerite
Formula:
K2Mg(SO4)2 · 6H2O
Colour:
Colourless, white, reddish, yellowish, grayish; colourless in transmitted light.
Lustre:
Vitreous
Hardness:
2½
Specific Gravity:
2.028
Crystal System:
Monoclinic
Member of:
Name:
From the Greek for "bitter" and "part" in allusion to the presence of magnesium and was originally applied to material crystallized from an aqueous solution of mixed salts from Vesuvius fumaroles.
Picromerite Group.
Fresh picromerite is colorless. Specimens may dehydrate in collections within days to years (according to the conditions) to white, opaque leonite.
Picromerite-type compounds are labeled Tutton salts in chemistry.
Fresh picromerite is colorless. Specimens may dehydrate in collections within days to years (according to the conditions) to white, opaque leonite.
Picromerite-type compounds are labeled Tutton salts in chemistry.
Unique Identifiers
Mindat ID:
3206
Long-form identifier:
mindat:1:1:3206:9
IMA Classification of Picromerite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
K2Mg(S6+O4)2·6H2O
First published:
1855
Classification of Picromerite
7.CC.60
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
29.3.6.1
29 : HYDRATED ACID AND NORMAL SULFATES
3 : A2B(XO4)2·xH2O
29 : HYDRATED ACID AND NORMAL SULFATES
3 : A2B(XO4)2·xH2O
25.3.15
25 : Sulphates
3 : Sulphates of Mg
25 : Sulphates
3 : Sulphates of Mg
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 |
|---|---|---|
| Pmr | 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 Picromerite
Vitreous
Transparency:
Transparent
Colour:
Colourless, white, reddish, yellowish, grayish; colourless in transmitted light.
Comment:
Tints due to admixed materials
Streak:
White
Hardness:
2½ on Mohs scale
Cleavage:
Perfect
On {201}, perfect.
On {201}, perfect.
Density:
2.028 g/cm3 (Measured) 2.031 g/cm3 (Calculated)
Comment:
Measured on artificial material.
Optical Data of Picromerite
Type:
Biaxial (+)
RI values:
nα = 1.4607 nβ = 1.4629 nγ = 1.4755
2V:
Measured: 48° , Calculated: 46°
Max. Birefringence:
δ = 0.015
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
High (negative)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
r > v strong
Chemistry of Picromerite
Mindat Formula:
K2Mg(SO4)2 · 6H2O
Element Weights:
Crystallography of Picromerite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P2/b
Setting:
P2/a
Cell Parameters:
a = 9.066 Å, b = 12.254 Å, c = 6.128 Å
β = 104.78°
β = 104.78°
Ratio:
a:b:c = 0.74 : 1 : 0.5
Unit Cell V:
658.26 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Short prismatic [001]. Crusts on other salts; also massive.
Crystal Structure
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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) |
|---|---|---|---|---|---|---|---|
| 0004776 | Picromerite | Bosi F, Belardi G, Ballirano P (2009) Structural features in Tutton's salts K2[M2+(H2O)6](SO4)2, with M2+= Mg, Fe, Co, Ni, Cu, and Zn American Mineralogist 94 74-82 |  | 2009 | synthetic | 0 | 293 |
| 0010626 | Picromerite | Kannan K K, Viswamitra M A (1965) Crystal structure of magnesium potassium sulfate hexahydrate MgK2(SO4)2*6(H2O) Zeitschrift fur Kristallographie 122 161-174 | | 1965 | synthetic | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.16 Å | (85) |
| 4.06 Å | (95) |
| 3.71 Å | (100) |
| 3.16 Å | (40) |
| 3.06 Å | (70) |
| 2.964 Å | (60) |
| 2.813 Å | (40) |
Comments:
Powder data from synthetic material.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) | |
| Stage 7: Great Oxidation Event | <2.4 |
| 45a : [Sulfates, arsenates, selenates, antimonates] | |
| 45b : [Other oxidized fumarolic minerals] | |
| 47a : [Near-surface hydration of prior minerals] | |
| 47b : [Sulfates and sulfites] | |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 55 : Anthropogenic mine minerals | |
| 56 : Slag and smelter minerals (see also #51 and #55) |
Geological Setting:
In kainite zones of some oceanic salt deposits.
Type Occurrence of Picromerite
Place of Conservation of Type Material:
No designated type material.
Geological Setting of Type Material:
Active volcanic fumaroles.
Synonyms of Picromerite
Other Language Names for Picromerite
Dutch:Picromeriet
Italian:Picromeride
Russian:Пикромерит
Simplified Chinese:软钾镁矾
Spanish:Picromerita
Traditional Chinese:軟鉀鎂礬
Relationship of Picromerite to other Species
Member of:
Other Members of Picromerite Group:
| Boussingaultite | (NH4)2Mg(SO4)2 · 6H2O | Mon. 2/m : P21/b |
| Cyanochroite | K2Cu(SO4)2 · 6H2O | Mon. 2/m : P21/b |
| Katerinopoulosite | (NH4)2Zn(SO4)2 · 6H2O | Mon. 2/m : P21/b |
| Mohrite | (NH4)2Fe(SO4)2 · 6H2O | Mon. 2/m : P21/b |
| Nickelboussingaultite | (NH4)2Ni(SO4)2 · 6H2O | Mon. 2/m : P21/b |
| Nickelpicromerite | K2Ni(SO4)2 · 6H2O | Mon. 2/m : P21/b |
Common Associates
Associations Based on Photo Data:
| 19 photos of Picromerite associated with Halite | NaCl |
| 3 photos of Picromerite associated with Leonite | K2Mg(SO4)2 · 4H2O |
| 1 photo of Picromerite associated with Hexahydrite | Mg(H2O)6(SO4) |
| 1 photo of Picromerite associated with Konyaite | Na2Mg(SO4)2 · 5H2O |
| 1 photo of Picromerite associated with Blödite | Na2Mg(SO4)2 · 4H2O |
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 | Alum-(K) | KAl(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 | 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) | 19.4172% | 6,019 | 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
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 Picromerite
mindat.org URL:
https://www.mindat.org/min-3206.html
Please feel free to link to this page.
Please feel free to link to this page.
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External Links:
Mineral Dealers:
References for Picromerite
Reference List:
Hofmann, Wilhelm (1931) Die Struktur der Tuttonschen Salze. Zeitschrift für Kristallographie, Mineralogie und Petrographie, 78 (1-6). 279-333 doi:10.1524/zkri.1931.78.1.279
Kannan, K. K., Viswamitra, M. A. (1965) Crystal structure of magnesium potassium sulfate hexahydrate MgK2(SO4)2· 6H2O. Zeitschrift für Kristallographie, 122 (3). 161-174 doi:10.1524/zkri.1965.122.3-4.161
Hey, M. H. (1982) International Mineralogical Association: Commission on New Minerals and Mineral Names. Mineralogical Magazine, 46 (341) 513-514 doi:10.1180/minmag.1982.046.341.25
Localities for Picromerite
Showing 55 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.
Australia | |
| Harris et al. (2003) |
Austria | |
| Exel (1993) |
| Exel (1993) |
| Exel (1993) |
Cape Verde | |
| Silva et al. (2019) |
Chile | |
| Bandy (1938) +1 other reference |
China | |
| Sun Da-peng et al. (2002) |
| Shaoxiu (1991) |
| Dongsheng Hu (1990) +1 other reference |
| Shaoxiu (1991) +1 other reference |
| Xiying Zhang et al. (2007) |
| Mianping Zheng and Xifang Liu (2010) |
| Lichun Ma et al. (2010) |
| Tang (2005) | |
| Bingxiao (1992) |
| Huaning Qiu et al. (2000) |
Czech Republic | |
| Jan Hloušek |
| Matýsek et al. (2022) |
| Dokoupilova P. |
| Hršelová et al. (2013) | |
Germany | |
| A.Dietrich (2004) |
| Weiß (1990) |
| Weiß (1990) |
| Weiß (1990) |
| |
| Gerstenberg (n.d.) |
| Bode "Mineralien und Fundstellen BRD" ... |
| www.mineralienatlas.de (n.d.) |
| www.mineralienatlas.de (n.d.) |
| Palache et al. (1951) |
| Brockt et al. (2001) |
| Naumann |
| ... | |
| Witzke et al. (1998) |
| www.minrec.org (n.d.) |
Iran | |
| Mr. Maziar Nazari |
Italy (TL) | |
| Russo |
| Pelloux (1927) +1 other reference | |
| Pellino et al. (2025) | |
| Piccoli et al. (2007) |
| Neschen (n.d.) |
| www.cse.speleo.it |
Kazakhstan | |
| Pekov et al. (1993) |
Peru | |
| Ciesielczuk et al. (2013) |
Poland | |
| Wachowiak et al. (2016) |
| Kruszewski (2013) |
| Kruszewski (2012) |
UK | |
| Smith et al. (2014) |
| Kemp et al. (2016) | |
Ukraine | |
| Palache et al. (1951) |
| Palache et al. (1951) | |
| ... |
USA | |
| Hon et al. (2009) |
| Northrop et al. (1996) |
| Hawley +5 other references |
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Neuhof-Ellers potash works, Neuhof, Fulda, Kassel Region, Hesse, Germany