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CategorySulfate minerals
(repeating unit)
IMA symbolMrb[1]
Strunz classification7.CD.10
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Formula mass322.9 g/mol
ColorColorless, white, yellowish-white, greenish-white
Crystal habitGranular or well-formed coarse crystals
TwinningInterpenetration twinning on {001}; also on {100}
Cleavage{100} perfect, {001} poor, {010} poor
Mohs scale hardness1.5–2
DiaphaneityTransparent to translucent to opaque
Specific gravity1.49
Optical propertiesBiaxial (–), 2V=75.93°
Refractive indexnα = 1.396, nβ = 1.4103, nγ = 1.419
Birefringenceδ = 0.023
Other characteristicsNot radioactive, non-fluorescent

Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na2SO4·10H2O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is found around saline springs and along saline playa lakes. Associated minerals include gypsum, halite, thenardite, trona, glauberite, and epsomite.

Mirabilite is unstable and quickly dehydrates in dry air, the prismatic crystals turning into a white powder, thenardite (Na2SO4). In turn, thenardite can also absorb water and converts to mirabilite.

Mirabilite is used as a purgative in the Traditional Chinese medicine; in Mandarin, it is called máng xiāo. The name 'mirabilite' is based on the phrase "Sal mirabilis" (Latin for "wonderful salt") used by Johann Rudolph Glauber when he inadvertently synthesized mirabilite.[4][5]

Four mirabilite mounds were documented on the south shore of the Great Salt Lake, Utah, United States, in January 2020. These developed where springs surfaced along the beach, which had been exposed due to lower lake elevations, and cold air helped preserve the salt precipitate. This was documented by the Utah Geological Survey[6] as well as reported in the press.[7]

Crystal structure of mirabilite


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
  2. ^ Mineralienatlas
  3. ^ Mirabilite at Webmineral
  4. ^ a b Mirabilite at Mindat
  5. ^ Hill, James C. (1979). "Johann Glauber's discovery of sodium sulfate - Sal Mirabile Glauberi". Journal of Chemical Education. 56 (9): 593. Bibcode:1979JChEd..56..593H. doi:10.1021/ed056p593.
  6. ^ Mirabilite spring mounds mapped by the Utah Geological Survey at Great Salt Lake.
  7. ^ KUTV News: Rare salt formations appear along the great salt lake.

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