Syngenite
A valid IMA mineral species - grandfathered
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About Syngenite
Formula:
K2Ca(SO4)2 · H2O
Colour:
Colourless, white, light yellow; colourless in transmitted light
Lustre:
Vitreous
Hardness:
2½
Specific Gravity:
2.579 - 2.603
Crystal System:
Monoclinic
Name:
Named from the Greek 'συγγευής', related, for its chemical resemblance to polyhalite.
Type Locality:
Unique Identifiers
Mindat ID:
3856
Long-form identifier:
mindat:1:1:3856:6
IMA Classification of Syngenite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
K2Ca(S6+O4)2·H2O
First published:
1872
Classification of Syngenite
7.CD.35
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
D : With only large cations
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
D : With only large cations
29.3.1.1
29 : HYDRATED ACID AND NORMAL SULFATES
3 : A2B(XO4)2·xH2O
29 : HYDRATED ACID AND NORMAL SULFATES
3 : A2B(XO4)2·xH2O
25.4.8
25 : Sulphates
4 : Sulphates of Ca, Sr and Ba
25 : Sulphates
4 : Sulphates of Ca, Sr and Ba
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 |
|---|---|---|
| Sgn | 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 Syngenite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Colourless, white, light yellow; colourless in transmitted light
Streak:
White
Hardness:
2½ on Mohs scale
Cleavage:
Perfect
On {110} and {100} perfect; on {010} distinct.
On {110} and {100} perfect; on {010} distinct.
Fracture:
Conchoidal
Density:
2.579 - 2.603 g/cm3 (Measured) 2.597 g/cm3 (Calculated)
Optical Data of Syngenite
Type:
Biaxial (-)
RI values:
nα = 1.501 nβ = 1.5166 nγ = 1.5176
2V:
Measured: 28° , Calculated: 28°
Max. Birefringence:
δ = 0.017
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:
Low (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:
relatively strong
Comments:
Z = b; X ∧ c = –2.28°.
Chemistry of Syngenite
Mindat Formula:
K2Ca(SO4)2 · H2O
Element Weights:
Crystallography of Syngenite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/m
Setting:
P21/m
Cell Parameters:
a = 9.77 Å, b = 7.14 Å, c = 6.25 Å
β = 104.01°
β = 104.01°
Ratio:
a:b:c = 1.368 : 1 : 0.875
Unit Cell V:
423.02 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Crystalline crusts; lamellar aggregates. Crystals tabular {100} to prismatic [001], often exhibiting a variety of forms. Faces in the zone [001] striated vertically.
Twinning:
On {100} contact twinning common.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
View
CIF File Best | x | y | z | a | b | c
CIF File Best | x | y | z | a | b | c
Rotation
Stop | Start
Stop | Start
Labels
Console Off | On | Grey | Yellow
Console Off | On | Grey | Yellow
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) |
|---|---|---|---|---|---|---|---|
| 0010642 | Syngenite | Corazza E, Sabelli C (1967) The crystal structure of syngenite, K2Ca(SO4)2*(H2O) Zeitschrift fur Kristallographie 124 398-408 |  | 1967 | Kalasz, Galicia | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.855 Å | (100) |
| 3.165 Å | (75) |
| 5.71 Å | (55) |
| 2.741 Å | (55) |
| 2.827 Å | (50) |
| 9.49 Å | (40) |
| 4.624 Å | (40) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 7: Great Oxidation Event | <2.4 |
| 45a : [Sulfates, arsenates, selenates, antimonates] | |
| 46 : Near-surface hydrothermal alteration of minerals (see also #22) | |
| Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere | <0.6 |
| 52 : Guano- and urine-derived minerals | <0.4 |
Geological Setting:
Oceanic salt deposits; volcanic activity.
Type Occurrence of Syngenite
General Appearance of Type Material:
Druses in halite.
Associated Minerals at Type Locality:
Synonyms of Syngenite
Other Language Names for Syngenite
Common Associates
Associations Based on Photo Data:
| 4 photos of Syngenite associated with Halite | NaCl |
| 2 photos of Syngenite associated with Nickelpicromerite | K2Ni(SO4)2 · 6H2O |
| 2 photos of Syngenite associated with Thermessaite | K2AlF3(SO4) |
| 2 photos of Syngenite associated with Metavoltine | K2Na6Fe2+Fe3+6O2(SO4)12 · 18H2O |
| 2 photos of Syngenite associated with Hannayite | (NH4)2Mg3H4(PO4)4 · 8H2O |
| 2 photos of Syngenite associated with Ammoniotinsleyite | (NH4)Al2(PO4)2(OH) · 2H2O |
Related Minerals - Strunz-mindat Grouping
| 7.CD. | Argesite | (NH4)7Bi3Cl16 |
| 7.CD. | Campostriniite | (Bi3+,Na)3(NH4,K)2Na2(SO4)6 · H2O |
| 7.CD.05 | Matteuccite | NaHSO4 · H2O |
| 7.CD.10 | Mirabilite | Na2SO4 · 10H2O |
| 7.CD.15 | Lecontite | (NH4)Na(SO4) · 2H2O |
| 7.CD.20 | Hydroglauberite | Na10Ca3(SO4)8 · 6H2O |
| 7.CD.25 | Eugsterite | Na4Ca(SO4)3 · 2H2O |
| 7.CD.30 | Görgeyite | K2Ca5(SO4)6 · H2O |
| 7.CD.35 | Antofagastaite | Na2Ca(SO4)2 · 1.5H2O |
| 7.CD.35 | Koktaite | (NH4)2Ca(SO4)2 · H2O |
| 7.CD.40 | Gypsum | CaSO4 · 2H2O |
| 7.CD.45 | Chinleite-(Y) | NaY(SO4)2 · H2O |
| 7.CD.45 | Bassanite | Ca(SO4) · 0.5H2O |
| 7.CD.45 | Chinleite-(Nd) | NaNd(SO4)2 · H2O |
| 7.CD.45 | Chinleite-(Ce) | NaCe(SO4)2(H2O) |
| 7.CD.50 | Zircosulfate | (Zr,Ti)(SO4)2 · 4H2O |
| 7.CD.55 | Schieffelinite | Pb10Te6+6O20(OH)14(SO4)(H2O)5 |
| 7.CD.60 | Montanite | Bi2(TeO6) · nH2O |
| 7.CD.65 | Omongwaite | Na2Ca5(SO4)6 · 3H2O |
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) | 23.8103% | 7,381 | 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
Notes:
Soluble in H2O, with separation of gypsum.
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 Syngenite
mindat.org URL:
https://www.mindat.org/min-3856.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 Syngenite
Reference List:
Aruja, E. (1958) On the unit cell of calcium potassium sulphate hydrate: synthetic and natural syngenite. Mineralogical Magazine and Journal of the Mineralogical Society, 31 (242). 943-946 doi:10.1180/minmag.1958.031.242.07
Corazza, E.; Sabelli, C. (1967) The crystal structure of syngenite, K2Ca(SO4)2· H2O. Zeitschrift für Kristallographie, 124 (6). 398-408 doi:10.1524/zkri.1967.124.6.398
Gorogotskaya, L. I.; Podberezskaya, N. V.; Borisov, S. V. (1968) Refinement of the crystal structure of syngenite K2Ca(SO4)2 · H2O. Journal of Structural Chemistry, 9 (1). 69-72 doi:10.1007/bf00744028
Wieczorek-Ciurowa, Krystyna (1985) Topochemistry of thermal dehydration of syngenite K2Ca(SO4)2·H2O. Thermochimica Acta, 92. 485-487 doi:10.1016/0040-6031(85)85921-9
Onac, B. P., White, W. B., Viehmann, I. (2001) Leonite [K2Mg(SO4)2·4H2O], konyaite [Na2Mg(SO4)2·5H2O] and syngenite [K2Ca(SO4)2·H2O] from Tausoare Cave, Rodnei Mts, Romania. Mineralogical Magazine, 65 (1) 103-109 doi:10.1180/002646101550154
Kloprogge, J.Theo, Ding, Zhe, Martens, Wayde N., Schuiling, Roelof D., Duong, Loc V., Frost, Ray L. (2004) Thermal decomposition of syngenite, K2Ca(SO4)2·H2O. Thermochimica Acta, 417. 143-155 doi:10.1016/j.tca.2003.12.001
Localities for Syngenite
Showing 57 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 | |
| Benedetto et al. (1998) |
Australia | |
| Snow et al. (2014) |
| Caves: processes +1 other reference |
| Bridge (1974) |
| Bridge (1977) | |
Austria | |
| Exel (1993) |
Bolivia | |
| Bentz (2017) |
Botswana | |
| Martini (1996) +1 other reference |
Canada | |
| Greengrass et al. (1999) |
Chile | |
| SEM-EDS by Joy Desor +1 other reference |
| Luetcke (n.d.) | |
China | |
| Anthony |
| Shaoxiu (1991) |
| Shaoxiu (1991) |
| Yaoting Lin and Jinquan He (2004) |
| Xiyu Zheng and Shengsong Yu (1981) |
| Tang (2005) +1 other reference |
| Bingxiao (1992) |
Czech Republic | |
| Matýsek et al. (2026) |
| Varilová et al. (2011) |
France | |
| Eytier J.R. & Ch. et al. (2004) |
Germany | |
| Weiß (1990) |
| Weiß (1990) |
| Weiß (1990) |
| |
| Bode "Mineralien und Fundstellen BRD" ... |
| Gerstenberg (n.d.) |
| Weiß (1990) |
| Blaß et al. (1995) |
| Hentschel (2014) +1 other reference |
| Frenzel (1964) |
| Frenzel (1964) | |
| Hentschel (2014) +1 other reference |
| Brockt et al. (2001) |
| Witzke et al. (1998) |
| Palache et al. (1951) |
Italy | |
| D’Angeli et al. (2022) |
| Russo +2 other references |
| Cavarretta et al. (1982) +2 other references |
| Sbacchi et al. (2019) |
Japan | |
| Seki et al. (1987) |
Kazakhstan | |
| Pekov et al. (1993) |
Kenya | |
| Bowell et al. (1996) |
Namibia | |
| Martini et al. (1999) |
North Macedonia | |
| Đorđević et al. (2024) |
Poland | |
| Marszałek +2 other references |
Romania | |
| - (2001) |
Russia | |
| Pavel M. Kartashov analytical data (2011) |
| Shablinskii et al. (2022) |
| kimberlites of Udachnaya-East pipe (Siberia) +1 other reference |
UK | |
| Kemp et al. (2016) |
Ukraine (TL) | |
| Palache et al. (1951) +2 other references |
| Palache et al. (1951) |
USA | |
| Palache et al. (1951) |
| Albemarle Corporation |
| Northrop et al. (1996) |
| Hawley +5 other references |
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Glückauf mine, Sondershausen, Kyffhäuser District, Thuringia, Germany