Euchroite Cu2(AsO4)(OH)•3H2O is among the most beautiful Slovak secondary minerals. Its name was derived from the Greek word euchros, meaning beautifully coloured. Euchroite was first described in 1823 by J. F. August Breithaupt (1791 – 1873), a professor of mineralogy at the Freiberg Mining Academy, however, this came from the world-renowned deposit at Svätodušná. Euchroite is a supergene mineral that crystallises as an orthorhombic crystal. It is copper arsenate that forms isometric, tabular, short-prism crystals of mostly emerald green or, less frequently, a blue-green colour. It is normally transparent with a glassy gloss; however, typically some crystals, such as isomeric crystals...