Blödite
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Blödite or bloedite is a hydrated sodium magnesium sulfate mineral with the formula Na₂Mg(SO₄)₂·4H₂O. The mineral is clear to yellow in color often darkened by inclusions and forms monoclinic crystals. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Prismatic to equant crystals, granular, massive
Crystal system: Monoclinic
Mohs scale hardness: 2.5–3
Refractive index: nα = 1.483, nβ = 1.486, nγ = 1.487