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Gaylussit - Lagunillas, Venezuela.jpg
Gaylussite - Lagunillas, Venezuela
Category Carbonate mineral
(repeating unit)
Strunz classification 5.CB.35
Crystal system Monoclinic
Crystal class Prismatic (2/m)
Color Colorless, white, yellow, and grey
Crystal habit Tabular prismatic crystals also granular
Crystal symmetry Monoclinic
H-M symbol: (2/m)
Space group: I2/a
Cleavage perfect [110]
Fracture Conchoidal, brittle
Mohs scale hardness 2.5
Luster vitreous
Streak white
Specific gravity 1.93 - 1.99
Optical properties Biaxial (-)
Refractive index nα = 1.444 nβ = 1.516 nγ = 1.523
Birefringence δ = 0.079
Solubility decomposes in water
Other characteristics efflorescent
References [1][2][3]

Gaylussite is a carbonate mineral, a hydrated sodium calcium carbonate, formula Na2Ca(CO3)2·5H2O. It occurs as translucent, vitreous white to grey to yellow monoclinic prismatic crystals. It is an unstable mineral which dehydrates in dry air and decomposes in water.[1]

It is formed as an evaporite from alkali lacustrine waters. It also occurs rarely as veinlets in alkalic igneous rocks.[1] It was first described in 1826 for an occurrence in Lagunillas, Merida, Venezuela. It was named for French chemist Joseph Louis Gay-Lussac (1778–1850).[2]

The mineral has been recently reported from drill core in Lonar lake in central India.[4]


  1. ^ a b c Handbook of Mineralogy
  2. ^ a b Mindat
  3. ^ Webmineral
  4. ^ Anoop et al., Palaeoenvironmental implications of evaporative gaylussite crystals from Lonar Lake, central India, Journal of Quaternary Science, V., Issue 4, pp. 349–359, May 2013