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(mineralogy) An evaporite, consisting of hydrated magnesium sulphate

Colorless, grayish-white or yellowish – Massive, granular; rarely as pyramidal crystals – Contact on {001}, polysynthetic about [110] – {110} and {111} perfect – Uneven – Fragile – 3.5 – Vitreous to dull – White – Transparent to translucent – 2.57 – Biaxial (+) – Nα = 1.520 nβ = 1.533 nγ = 1.584 – Δ = 0.064 – 55° – R > v, moderate – In water.