Gaylussite - Lagunillas, Venezuela
|Crystal class||Prismatic (2/m)|
|Color||Colorless, white, yellow, and grey|
|Crystal habit||Tabular prismatic crystals also granular|
H-M symbol: (2/m)
Space group: I2/a
|Mohs scale hardness||2.5|
|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|
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).
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