KCu3(V2O7)(OH)2Cl

 

Engelhauptite was approved by IMA with no 2013-009. Former name was UM (unknown mineral) K-Cu-Al-Cl-Vanadanate if you read older literature. Engelhauptite is linked to Volborthite with identical molecular structure [Cu3(V2O7)(OH)2]. If the channels of Volborthite in between are filled with H2O here at Engelhauptite they be taken with K and Cl anions. Thatr means the chemical content is different. (quote and thanks to G.Blaß)

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Engelhauptite was found first time at volcano Kahlenberg "Auf'm Kopp" near Neroth, Eifel, Germany. In paragenetic with high content of Cu most items contents also Allophane/Chrysocolla, Wulfenite, yellow Volborthite and also Malachite. For more details and all EDX values please look in Eifel-CD by G. Blaß.  

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Items of Engelhauptite are very rare, best ones contains flowers of yellow orange crystals, other have only some small clusters of crystals 0.12 mm.