Magnesium sulfate constituents of evaporitic potassium-magnesium (K-Mg) salts deposits. Bright spots observed by the Dawn Spacecraft in Occator Crater on the dwarf planet Ceres are most consistent with reflected light from magnesium sulfate hexahydrate. Almost all known mineralogical forms of MgSO are hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO·7HO, was recently recognized. Both are, however, not the highest known hydrates of MgSO, due to the recent terrestrial find of meridianiite, MgSO·11HO, which is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydrates—pentahydrite, starkeyite, and especially
Magnesium oxychloride It can be prepared by calcination of magnesium hydroxycarbonate ·4 at about 600 °C. (Higher temperatures increase particle size leading to lower reaction rate.) It is believed that, during the reaction, the magnesium oxide is continuously hydrated and dissolved, helped by the slightly acidic character of the magnesium chloride solution. The acidity is attributed to hydrolysis of the magnesium hexahydrate cations: The protons (which are actually hydrated, e.g. as ) make the solution acidic; the pH varies from 6.5 to 4.7 as the concentration of increases from 30% to 70% (weight basis). The protons then react with and dissolve the