Syngenite
Syngenite is an uncommon potassium calcium sulfate mineral with formula K2Ca(SO4)2·H2O. It forms as prismatic monoclinic crystals and as encrustations.
| Syngenite | |
|---|---|
Tapering crystal of syngenite (size: 4.4 × 1.3 × 0.6 cm) | |
| General | |
| Category | Sulfate mineral |
| Formula (repeating unit) | K2Ca(SO4)2·H2O |
| IMA symbol | Sgn |
| Strunz classification | 7.CD.35 |
| Dana classification | 29.3.1.1 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/m |
| Unit cell | a = 9.77 Å, b = 7.14 Å c = 6.25 Å; β = 104.01°; Z = 2 |
| Identification | |
| Color | Colorless, milky white to faintly yellow due to inclusions |
| Crystal habit | Tabular to prismatic crystals, lamellar aggregates and crystalline crusts |
| Twinning | Common on {101} contact twins |
| Cleavage | Perfect on {110} and {100}, distinct on {010} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.579–2.603 |
| Optical properties | Biaxial (−), colorless (transmitted light) |
| Refractive index | nα = 1.501 nβ = 1.517 nγ = 1.518 |
| Birefringence | δ = 0.017 |
| 2V angle | Measured: 28° |
| Solubility | Partially dissolves in water |
| References | |
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