Images
Formulae:
Nováčekite-I Mg(UO2)2(AsO4)2.12H2O
Nováčekite-II Mg(UO2)2(AsO4)2.10H2O
Arsenate, uranyl mineral,
autunite group, forms a series with
saléeite
Nováčekite-I is very unstable under ambient conditions and quickly dehydrates to nováčekite-II, in part also to
metanováčekite. "Nováčekite" specimens in collections mostly
seem to be either nováčekite-II or metanováčekite
(Mindat).
Crystal System: Monoclinic
Specific gravity: 3.25 to 3.70
Hardness: 2 to 2½
Streak: Very pale yellow
Colour: Pale yellow, yellow
Luminescence: Fluoresces dull green to bright lemon yellow in both long wave and short wave UV
RADIOACTIVE
Environments
Sedimentary environments
Hydrothermal environments
Nováčekite occurs in the oxidised zone of uranium-bearing polymetallic
hydrothermal mineral deposits
(Webmin).
Localities
At the Michael Mine, Weiler, Seelbach, Seelbach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany,
infiltrating oxidising, U6+-bearing fluids reacted under ambient
conditions with galena and
native arsenic, forming a variety of
U6+ (±Pb)-bearing
arsenates such as hügelite,
hallimondite, zeunerite,
heinrichite or novacekite together with
uranium-free minerals like mimetite
or anglesite. Some parts of the vein were enriched to
uranium concentrations of up to 1 wt% by this
supergene process. Reduced
(hypogene) uranium
phases like uraninite were never observed
(AM 105.727–744).
From Schneeberg, Erzgebirgskreis, Saxony, Germany, two specimens were found of nováčekite. The first
specimen comprised a small piece of deeply altered, quartz and
limonite vein material that was coated and veined by
secondary uranium
minerals. The nováčekite was
present as a small area, apparently a filled cavity, as a platy, cleavable mineral of a straw-yellow colour.
Small irregular flakes of zeunerite were present around the borders of
the mass of nováčekite and represent the first deposition on the cavity walls. Small groups of crystals
of zeunerite were present elsewhere on the specimen together with
tufted crusts of uranophane.
The second specimen comprised a small, friable mass of vein material, light brown in colour and composed largely
of limonite and quartz with
cavities lined or filled completely by indistinct straw-yellow to lemon-yellow crystals of nováčekite.
The veinlets are bordered by green crystals of zeunerite, which
formed earlier than the nováčekite, and some of the nováčekite crystals show intergrown
cores of zeunerite in parallel orientation
(AM 36.680-686).
At Wheal Owles, Botallack, St Just, Cornwall, England, UK, nováčekite is associated with
chalcopyrite,
arsenopyrite and sphalerite
(HOM).
At the Woodrow area, Laguna Reservation, Valencia County, New Mexico, nováčekite, straw yellow in
colour, coats an iron-stained friable sandstone, and forms a
series with saléeite
(AM 39.675-676).
In the Wichita Mountains, Kiowa county, Oklahoma, USA , nováčekite occurs in recent sedimentary deposits in
a friable red sandstone. Small cavities
in the sandstone are filled with nováčekite crystals
along with limonite, malachite,
calcite and quartz grains
(AM 41.152-153).
At the Cherkasar U Deposit, Pap, Chatkal-Kuraminskii Range, Namangan Region, Uzbekistan, nováčekite is
associated with schoepite,
paraschoepite,
arsenuranylite,
metazeunerite and
uranospinite
(HOM).
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