Gaylussite

Gaylussite
Gaylussite - Lagunillas, Venezuela
General
Category	Carbonate mineral
Formula (repeating unit)	Na2Ca(CO3)2·5H2O
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

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.

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

The mineral has been recently reported from drill core in Lonar lake in Buldhana district, Maharashtra, India. Lonar lake was created by a meteor impact during the Epoch and it is the only known hyper velocity impact crater in basaltic rock anywhere on Earth.