Epsomite, Epsom salt, or magnesium sulfate heptahydrate, is a hydrousmagnesium sulfate mineral with formula MgSO4·7H2O.
Physical properties
Epsomite crystallizes in the orthorhombic system. The normal form is as massive encrustations, while acicular or fibrous crystals are rarely found. It is colorless to white with tints of yellow, green and pink. It is a soft mineral with variable Mohs hardness around 2.0~2.5, and it has a low specific gravity of 1.67 g/ml.[5]
It is readily soluble in water, and absorbs water from the air. It converts to hexahydrate with the loss of one water molecule and a switch to monoclinic structure.[5]
It was first systematically described in 1806 for an occurrence near Epsom, Surrey, England, after which it was named.[5] It has been also referred to as "cave cotton" when in its fibrous form.[6]
Naturally occurring epsomite in caverns can potentially produce particulates of inhalable size, and may contain significant amounts of toxic impurities.[6][8]
Uses
Epsom salt is commonly sold as the main ingredient in bath salt, with additives such as glycerin (used as a humectant) and fragrances. The purpose of bath salts is mostly to make the bathing experience more enjoyable and serve as a vehicle for cosmetics, though they are said to improve cleaning and aid in exfoliation.[9]
Research on topical magnesium (for example Epsom salt baths) is very limited.[10] The trade organization 'Epsom Salt Council' recommends bathing 2 or 3 times/week, using 500–600 g (18–21 oz) Epsom salts each time.[11]
Gallery
Crystal structure of epsomitePhotomicrograph of epsomite fibers magnified 300 times, from a sample found on a wall of a former limestone quarry cavern in Ohio[6]