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Formula: (Ca,K,Ba)(V5+,V4+)8O20.3H2O
Vanadate,
straczekite group,
barium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.09 to 3.29 measured, 3.21 calculated
Hardness: 1 to 2
Streak: Greenish black
Colour: Green-black
Environments
Sedimentary environments
Hydrothermal environments
Localities
At the type locality, the North Wilson pit, Union Carbide Mine, Wilson Springs, Garland County, Arkansas, USA,
straczekite is an uncommon secondary mineral, in seams
in argillaceous gangue, in
vanadium-rich
alkalic igneous and metamorphosed sedimentary rocks.
It is found in seams as fibrous, greenish black, foliated masses up to 1 cm across. Individual fibres are opaque and up to
0.5 mm long. Very thin flakes, in transmitted light, are yellowish green. The fibres have a greenish black streak and a
greasy black lustre. Associated minerals include hewettite,
duttonite, fervanite,
schoderite and
metaschoderite
(AM 70.877, HOM).
At the Lichtenberg Absetzer dump, Kauern, Greiz District, Thuringia, Germany, the
calcium-vanadate minerals
sincosite, simplotite and
straczekite were observed at the mine dump
(AM 86.9.1081–1086).
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