MgSO4
Magnesium sulfate · magnesium sulphate, anhydrous magnesium sulfate, sulfuric acid magnesium salt
Magnesium sulfate (MgSO4) is an inorganic salt made of magnesium cations and sulfate anions. It is a wide-band-gap insulating solid. Anhydrous MgSO4 has several polymorphs: orthorhombic alpha-MgSO4 is the stable form at ambient conditions, and beta-MgSO4 is a high-temperature form. Chemists know it as a drying agent for organic solutions, and its heptahydrate is sold as Epsom salt.
About Magnesium sulfate
What is MgSO4 and what structure does it have?
MgSO4 is an ionic alkaline-earth sulfate made of divalent magnesium cations and tetrahedral sulfate anions. Anhydrous MgSO4 has orthorhombic polymorphs. Alpha-MgSO4 (space group Cmcm, the CrVO4-type structure) is the stable form at ambient conditions. Beta-MgSO4 (space group Pbnm) is a high-temperature form. In both, MgO6 octahedra are linked through corner-sharing SO4 tetrahedra. MgSO4 also forms a large series of hydrates, the best known being the monoclinic monohydrate kieserite and the orthorhombic heptahydrate epsomite. Calculations put anhydrous MgSO4 at the thermodynamic ground state for this composition.
What is magnesium sulfate used for?
Magnesium sulfate is used in laboratory chemistry, agriculture, and medicine. The anhydrous form is a common drying agent in organic synthesis because it takes up water strongly. The hydrated forms, such as Epsom salt, are used as fertilizer to correct magnesium and sulfur deficiencies in crops. In medicine, it is given by mouth as a laxative and intravenously as an anticonvulsant. It is also used as a brewing salt and as a coagulant in food processing, for example in making tofu. Researchers are also studying its hydration–dehydration cycle for seasonal thermochemical heat storage.
How stable and synthesizable is MgSO4?
MgSO4 is thermodynamically stable and easy to prepare. It can be made by reacting sulfuric acid with magnesium oxide, magnesium hydroxide, or magnesium carbonate, then dehydrating the product. The anhydrous phase is strongly hygroscopic and picks up moisture from the air to form hydrates such as the monohydrate and heptahydrate. Heating the hydrates drives off water step by step until the anhydrous salt remains. At much higher temperatures, it decomposes into magnesium oxide and sulfur oxides.
Is MgSO4 an insulator or a conductor?
MgSO4 is an electronic insulator with a wide band gap. The Mg2+ cation and the sulfate anion both have closed-shell electronic configurations, so there are no partially filled bands to carry current. The crystalline solid does not conduct electricity, and it is colorless because it does not absorb visible light. When it dissolves in water, it splits into free ions, and the resulting solution conducts electricity.
How does MgSO4 compare to related sulfates?
Among the common alkaline-earth sulfates (magnesium through barium), MgSO4 has the smallest cation. It is highly soluble in water and forms many crystalline hydrates. Calcium sulfate is much less soluble and occurs as gypsum (the dihydrate) and anhydrite. Strontium sulfate (celestine) is only sparingly soluble, and barium sulfate (barite) is practically insoluble. Beryllium sulfate, with an even smaller cation, is also highly soluble.
Key Properties
Cross-validated computational properties for Magnesium sulfate, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of MgSO4. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for MgSO4, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 6.11 | 0.0000 | -2.274 | — |
| Cmcm (No. 63) | orthorhombic | 6.05 | 0.0000 | -2.071 | — |
| Cmcm (No. 63) | orthorhombic | 5.49 | 0.0000 | -6.662 | 3.04 |
| — | — | 5.90 | 0.0007 | -2.273 | — |
| Pnma (No. 62) | orthorhombic | 5.54 | 0.0053 | -6.657 | 2.95 |
| Pnma (No. 62) | orthorhombic | 6.11 | 0.0070 | -2.063 | — |
| — | — | 5.63 | 0.0132 | -2.260 | — |
| — | — | 5.98 | 0.0291 | -2.244 | — |
| — | — | 0.00 | 0.0309 | -2.243 | — |
| — | — | 6.02 | 0.0614 | -2.212 | — |
| — | — | 0.00 | 0.1138 | -2.160 | — |
| P21/c (No. 14) | monoclinic | 0.36 | 0.7923 | -5.870 | 2.24 |
Synthesis Routes
Literature-extracted synthesis procedures targeting MgSO4.
Applications
Where Magnesium sulfate is used.
Patent Landscape
1 patent reference MgSO4 or close compositional variants.
| Patent | Title | Assignee | Granted |
|---|---|---|---|
| 4195070 | Preparation of a MgCl.sub.2 solution for Nalco's MgCl.sub.2 process from MgSO.sub.4 and other MgSO.sub.4 salts | — | — |
Frequently Asked Questions
Common questions about Magnesium sulfate, answered from cross-validated data and the published literature.
Is anhydrous MgSO4 the same thing as Epsom salt?
No. Epsom salt is magnesium sulfate heptahydrate (MgSO4·7H2O). Anhydrous MgSO4 contains no water of crystallization.
Is magnesium sulfate soluble in water?
What happens when you heat MgSO4 hydrates?
Why is anhydrous MgSO4 commonly used in organic chemistry?
Does solid MgSO4 conduct electricity?
What is MgSO4?
What is MgSO4 used for?
What is the band gap of MgSO4?
Is MgSO4 a metal, semiconductor, or insulator?
Is MgSO4 thermodynamically stable?
What is the crystal structure of MgSO4?
What is the density of MgSO4?
How many polymorphs of MgSO4 are known?
How is MgSO4 synthesized?
What elements does MgSO4 contain?
Where does the data for MgSO4 come from?
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- cod — Data from the Crystallography Open Database (crystallography.net/cod/). Cite: Grazulis et al., J. Appl. Cryst. 42, 726 (2009). (CC0-1.0)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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