A theory about a mineral with this anion (“AN-eye-on”) claims that it forms from a three-stage self-aggregation of bassanite, which also has this anion. It’s not hydroxide, but jarosite is a common iron precipitate with this anion formed from acid mine drainage. Minerals (15[1])with this anion sometimes appear in so-called “desert rose” formations when found in arid sandy environments. Along with carbonates, minerals with this polyatomic anion are the most common (*) marine evaporites. (10[1])Barite contains this anion that is found in the primary mineral constituent of New Mexico’s white sand dunes. Plaster of (-5[1])paris is formed from heating a polymorph of anhydrite with this anion that defines a 2 on the Mohs mineral hardness scale. Along with calcium, gypsum contains this anion. Epsom salt comprises magnesium and—for 10 points—what anion with chemical formula SO4 2- ■END■ (10[1])