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Tapering crystal of syngenite (size: 4.4 × 1.3 × 0.6 cm)
CategorySulfate mineral
(repeating unit)
IMA symbolSgn[1]
Strunz classification7.CD.35
Dana classification29.3.1.1
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Unit cella = 9.77 Å, b = 7.14 Å
c = 6.25 Å; β = 104.01°; Z = 2
ColorColorless, milky white to faintly yellow due to inclusions
Crystal habitTabular to prismatic crystals, lamellar aggregates and crystalline crusts
TwinningCommon on {101} contact twins
CleavagePerfect on {110} and {100}, distinct on {010}
Mohs scale hardness2.5
DiaphaneityTransparent to translucent
Specific gravity2.579–2.603
Optical propertiesBiaxial (−), colorless (transmitted light)
Refractive indexnα = 1.501 nβ = 1.517 nγ = 1.518
Birefringenceδ = 0.017
2V angleMeasured: 28°
SolubilityPartially dissolves in water

Syngenite is an uncommon potassium calcium sulfate mineral with formula K2Ca(SO4)2·H2O. It forms as prismatic monoclinic crystals and as encrustations.

Discovery and occurrence[edit]

It was first described in 1872 for an occurrence as druse on halite in the Kalusa Salt deposit, Ivanovo-Frankovsk Oblast', Ukraine.[3] The name is from Greek 'συγγενής' (related) due to its chemical similarity to polyhalite.[4][3]

It occurs in marine evaporite deposits as a diagenetic phase. It also forms as a volcanic sublimate, as vein fillings in geothermal fields and in caves where it is derived from bat guano. It occurs in association with halite and arcanite in salt deposits; and with biphosphammite, aphthitalite, monetite, whitlockite, uricite, brushite and gypsum in cave environments.[2]

It is also found in hardened cement which has relatively higher amount of potassium. [5]


Syngenite can be artificially produced by the action of a potassium sulfate solution on gypsum.[6]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Handbook of Mineralogy
  3. ^ a b c Syngenite on
  4. ^ a b Syngenite data on Webmineral
  5. ^ a b Atkins M, Glasser FP, Moron IP, Jack JJ, 1993. Thermodynamic modelling of blenede cemnts at elevated temperature (50–90 °C).
  6. ^ Ennaciri, Yassine; Alaoui-Belghiti, Hanan El; Bettach, Mohammed (May 2019). "Comparative study of K2SO4 production by wet conversion from phosphogypsum and synthetic gypsum". Journal of Materials Research and Technology. 8 (3): 2586–2596. doi:10.1016/j.jmrt.2019.02.013. Open access icon


  • Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 442-444.