By Jennifer Uhl | Updated August 30, 2022
Epsom salt, chemically known as magnesium sulfate (MgSO₄), is a versatile mineral used in medicine, agriculture, and aquaculture. It naturally occurs in mineral deposits and coal‑burning sites.
In its most common hydrate form, MgSO₄·7H₂O, Epsom salt crystallizes in a monoclinic lattice. The crystals are typically larger than table salt, which is why they are often sold as coarse grains for bath use or aquarium salt mixes.
When dry (anhydrous), the compound is hygroscopic, readily absorbing moisture from the air. The anhydrous salt has a melting point of 1124 °C and a molar mass of 120.366 g mol⁻¹.
Magnesium sulfate has the molecular formula MgSO₄. In the monohydrate form (MgSO₄·H₂O), it exhibits a pH of 5.5–6.5 and melts at 200 °C. The anhydrous form is highly soluble in water, with a solubility of 26.9 g per 100 mL.
• Gardening & agriculture: Supplies magnesium to plants, improving yields for crops such as roses, potatoes, tomatoes, cannabis, and peppers.
• Personal care: Added to bath water or foot baths to soothe sore muscles; the skin can absorb magnesium sulfate, helping reduce inflammation.
• Aquaculture: Marine aquariums use Epsom salt to support the calcification of stony corals.
For more detailed information, consult resources such as the PubChem entry for magnesium sulfate or the US EPA chemical database.
