Hauyn crystals from the German volcano Laacher See (photo: Stefan Wolfsried)
Hauyn is a blue mineral, found f.e. in the pumice of the Laacher See eruption in Germany
Hauyne, haüyne or hauynite is a tectosilicate mineral with sulfate and chloride with formula: (Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2. It is a feldspathoid and a member of the sodalite group. Hauyne crystallizes in the isometric system forming translucent, vitreous typically twinned crystals with highly variable color (blue, white, grey, yellow, green, pink). It has a Mohs hardness of 5 to 6 and a specific gravity of 2.4 to 2.5.
Hauyne was first described in 1807 from samples at Vesuvius Mount Somma, Italy. It was named for the French crystallographer, Rene Just Hauy (1743-1822). It occurs in silica deficient igneous rocks in a wide variety of locations.
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