White shiny crystals of the very rare mineral eugsterite in a matrix of glauberite from a locality in Kenya very close to the type locality: Kalacha, Turkana County, Kenya. — Photo: David Hospital · CC BY-SA 4.0
Eugsterite
Eugsterite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Na₄Ca(SO₄)₃·2H₂O.
Key properties: specific gravity 2.5; optically biaxial.
IMA symbol Egt, IMA status: approved, named in 1980.
Occurs as evaporative crusts in carbonate-poor soil, playa sediment and around an active boron-rich spring.
It is found associated with Thénardite, halite, blödite, gypsum, glauberite, nesquehonite, admontite.
The mineral was named to honor Professor Hans Peter Eugster (1927–1985), Swiss–American mineralogist, Johns Hopkins University, Baltimore, Maryland, USA, who studied the mineralogy of saline lakes.