Goslarite is a hydrous zinc sulfate mineral with formula: ZnSO4·7H2O. It is a secondary mineral which develops after primary zinc minerals within the zone of oxidation and in old sphalerite mine workings. It is unstable at the surface and dehydrates readily. It is transparent to translucent and variable in color, ranging from colorless, green, blue to brown. It crystallizes in the orthorhombic system and forms acicular crystals, stalactitic forms and massive clumps. It has a Mohs hardness of 2 - 2.5 and a low specific gravity of only 2. Related minerals include epsomite (MgSO4·7H2O) and morenosite (NiSO4·7H2O).