Picromerite
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Picromerite is a mineral from the class of hydrous sulfates lacking additional anions, and containing medium to large cations according to the Nickel–Strunz classification. Wikipedia
Solubility: in cold water
Color: Colorless; white, grey, reddish, yellowish
Crystal class: Prismatic (2/m); (same H-M symbol)
Dana classification: 29.03.06.01
Density: 2.03
Formula (repeating unit): K2Mg(SO4)2·6H2O
Refractive index: nα = 1.461 nβ = 1.463 nγ = 1.476