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 with this anion sometimes appear in so-called “desert rose” formations when found in arid sandy environments. Along with carbonates, minerals with this polyatomic (-5[1])anion are the most common (*) marine (10[1])evaporites. Barite contains this anion that is found in the primary mineral constituent of New Mexico’s white sand dunes. (-5[2])Plaster of paris is formed from heating a polymorph (-5[1])of anhydrite with this anion that defines a 2 on the Mohs (10[1])mineral hardness scale. Along with calcium, gypsum (-5[1])contains this anion. Epsom salt comprises magnesium and—for 10 points—what anion with chemical formula SO4 (10[1])2- ■END■ (10[4]0[1])