Eugsterite

eugsterite

thenardite

halite

nesquehonite

Images

Formula: Na₄Ca(SO₄)₃.2H₂O
Hydrated sulphate
Crystal system: Monoclinic
Specific gravity: Less than 2.5 measured
Hardness: 1 to 2
Streak: White
Colour: Colourless
Solubility: Soluble in water
Environments

Evaporite deposits

Eugsterite occurs as evaporative crusts in carbonate-poor soil, playa sediment and around an active boron-rich spring. Associated minerals include thénardite, halite, blödite, gypsum, glauberite, nesquehonite and admontite (HOM).

Localities

There are three co-type localities: Sindo, Homa Bay County, Kenya, Luanda, Vihiga County, Kenya and Karapinar, Karapınar District, Konya Province, Turkey

At the Bergwerk West Mine, Kamp-Lintfort, Wesel, Düsseldorf, North Rhine-Westphalia, Germany, white eugsterite has been found with yellow sideronatrite on coal (Mindat photo).
Eugsterite from the Bergwerk West Mine - Image

Sindo, Homa Bay County, Kenya (TL) and Luanda, Vihiga County, Kenya (TL). Salts of saline soils with efflorescences at the surface and groundwaters from which these salts have originated through evaporation have been sampled in some regions in Kenya. Most salts belong to the group of sodium carbonates and the waters are mainly of the Na-CO₃-SO₄-Cl- or Na-CO₃-Cl- type. In some sample sites, however, the groundwaters are carbonate-poor and they are of the Na-SO₄-Cl-type. The groundwaters of the places where eugsterite was found belong to this latter, carbonate-poor, type. Eugsterite has been found at two places along the shore of Lake Victoria, at Sindo and Luanda, where it is found as a surface mineral in association with thénardite and halite (AM 66.632-636).

At Kalacha, Marsabit County, Kenya, there are vast salt efflorescences and eugsterite is found in association with halite and thénardite (AM 66.632-636).

At Karapinar, Karapınar District, Konya Province, Turkey (TL), salt samples were taken in the Konya Basin. This basin, a former lake formed during the Tertiary (66 to 2.6 million years ago), consists of salt-affected clayey marl soils. The climate is semi-arid with cold moist winters and hot dry summers. The lowest parts are flooded in winter and when the surface water evaporates in summer vast salt crusts occur. In other parts of the basin which are not flooded, salts form at the surface through evaporation of the groundwater.
The salts in the basin are mainly sulphates and chlorides of sodium and magnesium. Sodium carbonates were found at only a few localities; these are devoid of eugsterite, which is commonly found in the other efflorescences. It occurs in the following associations:
eugsterite, halite, thénardite
eugsterite, blödite
eugsterite, halite, gypsum
eugsterite, halite, glauberite
eugsterite, halite, glauberite, thénardite, nesquehonite
The last association was found around the historical medicinal spring of Tiana. At the Karapina type locality, in summer the playa is covered with a flinty white salt crust which consists of halite, thénardite and eugsterite (AM 66.632-636).

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