Gaylussite

Gaylussite
General
Category	Carbonate mineral
Formula (repeating unit)	Na2Ca(CO3)2·5H2O
IMA symbol	Gyl [1]
Strunz classification	5.CB.35
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	I2/a
Identification
Color	Colorless, white, yellow, and grey
Crystal habit	Tabular prismatic crystals also granular
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	[2] [3] [4]

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. ^[2]

Discovery and occurrence

It is formed as an evaporite from alkali lacustrine waters. It also occurs rarely as veinlets in alkalic igneous rocks. ^[2] 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). ^[3]

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 ^[5] and it is one of only four known hyper-velocity impact craters in basaltic rock anywhere on Earth. ^{[6] [7]}

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
2. Handbook of Mineralogy
3. Mindat
4. Webmineral
5. "Geology". Government of Maharashtra . Gazetteers Department. Retrieved 2008-09-08.
6. 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.
7. 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