Epsomite

Epsomite is a mineral made of magnesium, sulfur, oxygen and water (magnesium sulfate heptahydrate, MgSO₄·7H₂O); more than half of its weight is water. It mostly forms white, feathery or cotton-like fibrous crusts on cave and mine walls, and its crystals are rare. It is very soft, dissolves easily in water and tastes bitter. The “Epsom salt” known as bath salts is this same substance; the name comes from the town of Epsom in Surrey, famous in the 17th century for its bitter spring water.

The uses below are for magnesium sulfate; today this substance is taken from natural sources such as dry lake beds, or made in factories. Bath salts: It is a traditional ingredient of bath salts, used especially in foot baths for tired feet. Medicine: In hospitals, under medical supervision, it is used to treat abnormal blood magnesium levels and constipation, and to reduce the risk of seizures in eclampsia during pregnancy.

It has a hardness of 2–2.5 on the Mohs scale. It is soft enough to scratch with a fingernail. Its specific gravity is 1.67–1.68 g/cm³.

Its best-known localities: Epsom, Surrey, England; Špania Dolina (Herrengrund), Banská Bystrica Region, Slovakia; Mammoth Cave, Kentucky, USA; Vesuvius, Campania, Italy; Oroville area (Kruger Mountain), Okanogan County, Washington, USA.

It is very soft (hardness 2–2.5) and very light (specific gravity 1.67–1.68): noticeably lighter than most common minerals. It mostly forms white, feathery or cotton-like fibrous crusts and tufts; good crystals are rare and reach 8 cm at most. It dissolves easily in water and tastes bitter (still, do not try to identify unknown minerals by tasting them). Other water-soluble sulfate crusts found in the same places (such as alunogen, pickeringite, halotrichite and melanterite) are often white and feathery too; they can be hard to tell apart by eye. A laboratory analysis is needed for certain identification.

On the “street to diamond” value ladder it sits on step 2 of nine: Raw material by the tonne. Epsomite is not an ore; the magnesium sulfate sold as Epsom salt is taken from natural sources such as dry lake beds or made in factories, and it is a cheap chemical. Collectors look for good crystals: crystals are rare (up to 8 cm), while most specimens are fibrous crusts. Because it dissolves in water and loses water and breaks down in dry air, clean and undamaged specimens are the more valuable ones.

In 17th-century England it was believed that drinking the bitter water of the Epsom spring was good for health; a shelter was built for invalids around the spring, and the town gradually became a spa. People who recommend Epsom salt for baths and foot baths believe that it relaxes tired muscles and reduces swelling, and that enough magnesium is absorbed through the skin in warm water. An Epsom salt bath is said to relieve stress and tension and help people relax. In health and beauty circles Epsom salt is recommended for “detox” baths and “detox” foot baths. There is no strong scientific evidence that Epsom salt baths work, and it has not been shown that a meaningful amount of magnesium passes through the skin in warm water. A dermatologist who spoke to National Geographic sums it up as “the skin is mostly a barrier, not a sponge”; any relaxation most likely comes from the warm water itself. Epsom salt taken by mouth is a real laxative, but too much can cause severe vomiting, diarrhoea, a drop in blood pressure and heart problems; people with open wounds should avoid the bath. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.