Black massive Straczekite on matrix; from: Union Carbide Mine, Wilson Springs, Garland County, Arkansas, USA. Photo and collection Fernando Brederodes. — Photo: Fernando Brederodes · CC0
Straczekite
Straczekite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Ca,K,Ba)(V⁵⁺,V⁴⁺)₈O₂₀·3H₂O.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Straczekite structural group.
Key properties: specific gravity 3.09–3.29; Greenish black streak; Greasy luster; optically biaxial.
IMA symbol Szk, IMA status: approved, named in 1983.
An uncommon secondary mineral, in seams in argillaceous gangue, in vanadium-rich alkalic igneous and metamorphosed sedimentary rocks (Wilson Springs, Arkansas, USA).
It is found associated with Hewettite, duttonite, fervanite, schoderite, metaschoderite (Wilson Springs, Arkansas, USA).
The mineral was named to honor John A. Straczek, Chief Geologist, Union Carbide Corporation.