Colorless; needles; ZnSO₄.7H₂O ; odorless; astringent, metallic taste; effloresces in air; sp gr, 1.9661; melting point, 50 degrees C if heated rapidly; soluble in water and in glycerol; insoluble in alcohol; and its solutions are acid to litmus. Used in preparing zinc chemicals. Orthorhombic; molecular weight, 287.54; sp gr, 1.957 (at 25 degrees C, referred to water at 4 degrees C) and ranges from 1.9 to 2.1; Mohs hardness, 2.0 to 2.5; melting point, 100 degrees C; loses 7H₂O on heating to 280 degrees C; and slightly soluble in alcohol and in glycerol. Occurs as the mineral goslarite, which is white or yellowish; formed by the oxidation of sphalerite (ZnS) in damp locations, esp. in the presence of iron sulfides.