syngenite

{{infobox mineral | name = Syngenite | boxwidth = | boxbgcolor = | image = Syngenite-291274.jpg | imagesize = | alt = | caption = Tapering crystal of syngenite (size: 4.4 × 1.3 × 0.6 cm) | category = Sulfate mineral | formula = K2Ca(SO4)2·H2O | IMAsymbol = Sgn | molweight = | strunz = 7.CD.35 | dana = 29.3.1.1 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/m | unit cell = a = 9.77 Å, b = 7.14 Å c = 6.25 Å; β = 104.01°; Z = 2 | color = Colorless, milky white to faintly yellow due to inclusions | colour = | 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 = 2.5 | luster = Vitreous | streak = White | diaphaneity = Transparent to translucent | gravity = 2.579–2.603 | density = | polish = | opticalprop = Biaxial (−), colorless (transmitted light) | refractive = nα = 1.501 nβ = 1.517 nγ = 1.518 | birefringence = δ = 0.017 | pleochroism = | 2V = Measured: 28° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Partially dissolves in water | impurities = | alteration = | other = | references = }}

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