Source : Webster's Revised Unabridged Dictionary (1913)

Tachhydrite \Tach*hy"drite\, n. [Gr. tachy`s quick + "y`dwr
   water. So named from its ready deliquescence.] (Min.)
   A hydrous chloride of calcium and magnesium occurring in
   yellowish masses which rapidly deliquesce upon exposure. It
   is found in the salt mines at Stassfurt.