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(Epsom salt), a mineral of the sulfate class having the molecular formula MgS04-7H20. Epsomite crystallizes in the orthorhombic system, with prismatic or acicular crystals. White or colorless, it has a glassy luster. Epsomite has a hardness of 2 to 2.5 on Mohs’ scale, and it has a density of 1,680 kg/m3. The mineral is soluble in water and has a bitter, salty taste. It is formed by the evaporation of brine from sulfate salt lakes with a high magnesium content. Epsomite has various uses (seeMAGNESIUMSULFATE).