The Collaborative International Dictionary
Tachhydrite
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.
Wiktionary
tachhydrite
n. (alternative form of tachyhydrite English)