Gaylussite

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]

Gaylussite
General
CategoryCarbonate mineral
Formula
(repeating unit)		Na2Ca(CO3)2·5H2O
Strunz classification5.CB.35
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupI2/a
Identification
ColorColorless, white, yellow, and grey
Crystal habitTabular prismatic crystals also granular
Cleavageperfect [110]
FractureConchoidal, brittle
Mohs scale hardness2.5
Lustervitreous
Streakwhite
Specific gravity1.93 - 1.99
Optical propertiesBiaxial (-)
Refractive indexnα = 1.444 nβ = 1.516 nγ = 1.523
Birefringenceδ = 0.079
Solubilitydecomposes in water
Other characteristicsefflorescent
References[1][2][3]

Discovery and occurrence

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, Mérida, Venezuela. It was named for French chemist Joseph Louis Gay-Lussac (1778–1850).[2]

The mineral has been recently (2014) reported from drill core in Lonar lake in Buldhana district, Maharashtra, India. Lonar lake was created by a meteor impact during the Pleistocene Epoch[4] and it is one of only four known hyper-velocity impact craters in basaltic rock anywhere on Earth.[5][6]

References
  1. Handbook of Mineralogy
  2. Mindat
  3. Webmineral
  4. "Geology". Government of Maharashtra. Gazetteers Department. Retrieved 2008-09-08.
  5. Deshpande, Rashmi (3 December 2014). "The Meteor Mystery Behind Lonar Lake". National Geographic Traveller Idia. National Geographic Group. Archived from the original on 6 January 2015. Retrieved 27 July 2015.
  6. 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


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