Epsomite

(mineralogy) MgSO₄·7H₂O A mineral that occurs in clear, needlelike, orthorhombic crystals; commonly, it is massive or fibrous; luster varies from vitreous to milky, hardness is 2-2.5 on Mohs scale, and specific gravity is 1.68; it has a salty bitter taste and is soluble in water. Also known as epsom salt.

A mineral with the chemical composition MgSO · 7H₂O. Epsomite, or epsom salt, occurs in clear, needle-like, orthorhombic crystals. More commonly it is massive or fibrous, although crystals from salt lakes on Kruger Mountain near Orville, Washington, are reported to be several feet long. Fracture is conchoidal. Luster varies from vitreous to silky. Hardness is 2–2.5 on Mohs scale and specific gravity is 1.68. The mineral has a salty bitter taste and is soluble in water. Epsomite is found as a capillary coating in limestone caves and in coal or metal mine galleries. It is also found associated with gypsum and in thin layers in salt deposits of oceanic origin or from salt lakes.

Environment

Cave walls, as a white efflorescence deposited by salt springs.

Usually not in crystals but in white hairlike or cottony efflorescences. Also in botryoidal masses and small prismatic crystals.

White. Luster silky, glassy to earthy; hardness 2-2Ɖ; specific gravity 1.7 (but water-soluble, so not readily determined); fracture conchoidal; cleavage 1 perfect and 2 less perfect. Brittle (artificial crystals) to cottony; translucent to transparent; bitter taste.

Hydrous magnesium sulfate (16.3% MgO, 32.5% SO ₃ , 51.2% H ₂ O).

Rapidly and completely water-soluble. Melts readily to a liquid in its own water of crystallization.

Its taste and ready solubility, together with its occurrence, are usually distinctive. Tests for sulfate (p. 171) tarnish silver.

In the U.S., epsomite's principle occurrences are as white efflorescences on the walls of limestone caves, where they are protected from solution by rain or much dampness. During droughts it has been found in large crystals in a lake-bed deposit on Kruger Mountain, Oroville, Washington. In some very dry localities, as in South Africa, it may form beds of considerable thickness, but in general it can be considered rare. It has also been found around fumaroles on Vesuvius lavas. The name is derived from its occurrence in the solution from a medicinal mineral spring at Epsom, England.

Epsomite
Epsomite formation in a New Mexico, cave
General
Category	Sulfate mineral
Chemical formula	MgSO4·7H2O
Strunz classification	VI/C.07
Dana classification	29.6.11.1
Identification
Color	White, grey, colorless, or pink, greenish
Crystal habit	Acicular to fibrous encrustations
Crystal system	Orthorhombic
Cleavage	{010} perfect {101} distinct
Fracture	Conchoidal
Luster	Vitreous
Diaphaneity	Transparent to translucent
Specific gravity	1.67 - 1.68
Optical properties	Biaxial (-)
Refractive index	nα = 1.433 nβ = 1.455 nγ = 1.461
References	[1][2]

Epsomite is a hydrous magnesium sulfate mineral with formula MgSO₄·7H₂O or simply MgSO₄. Epsomite forms as encrustations or efflorescences on limestone cavern walls and mine timbers and walls, as a volcanic fumaroles, and as rare beds in evaporate layers. It was first systematically described in 1806 for an occurrence near Epsom, Surrey, England, for which it was named.

Epsomite crystallizes in the orthorhombic system as rarely found acicular or fibrous crystals, the normal form is as massive encrustations. It is colorless to white with tints of yellow, green and pink. The Mohs hardness is 2 to 2.5 and it has a low specific gravity of 1.67.

Epsomite is the same as the household chemical, Epsom salt, and is readily soluble in water. It absorbs water from the air and converts to hexahydrite with the loss of one water molecule and a switch to monoclinic structure.

Related Minerals

• Kieserite (MgSO₄·H₂O) is less hydrated

References

1. ^ http://webmineral.com/data/Epsomite.shtml Webmineral data
2. ^ http://www.mindat.org/min-1393.html Mindat

• Mineral galleries

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