Images
Formula: Cu3(OH)2[(UO2)4O4(SO4)2].12H2O
or
Cu2+3(OH)2[(U6+O2)4O4(SO4)2].12H2O
Hydrated sulphate, uranyl mineral,
zippeite group
Crystal System: Triclinic
Specific gravity: 4.31 measured, 4.38 calculated (we expect the measured value to be less than the calculated value
since uranium, mass number 238, continuously alters to lead, mass number 207, by several stages of radioactive decay)
Colour: Moss-green
Luminescence: Green fluorescence under UV
RADIOACTIVE
Environments
Pseudojohannite is found in parageneses formed through the interaction of acidic sulphate mine drainage
waters with uraninite or uranyl
silicates
(Mindat).
Localities
At the Musonoi Mine, Kolwezi, Mutshatsha, Lualaba, DR Congo, light green pseudojohannite appears in
association with yellow uranopilite and orange-yellow
metaschoepite on a saccharoidal
quartz matrix containing many crosscutting veins of
kasolite, uranophane and
cuprosklodowskite. Other associated mineral species are relict
selenium-bearing digenite,
malachite, and a pale blue
brochantite. The pseudojohannite crystals measure up to 25 μm in
length, and are flattened along the cleavage plane. They coat several cm
The acid drainage waters probably result mainly from the oxidation of
selenium-bearing digenite, and
pseudojohannite subsequently forms through the reaction with oxidised
uranium-bearing minerals such as
kasolite, uranophane and
cuprosklodowskite
(AM 91.929-936).
Pseudojohannite from the Musonoi mine -
Image
At the type locality, the Rovnost Mine, Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic, to
date (2006), only one sample is known to contain pseudojohannite. In this sample, pseudojohannite
grows directly on strongly weathered uraninite containing
pyrite, tennantite and
chalcopyrite and is associated with
johannite, uranopilite and
gypsum. Pseudojohannite forms earthy moss-green, brittle aggregates
up to 5 mm in size, or coatings with an uneven surface, which are composed of very fine crystals with sizes between
1 and 10 μm
(AM 91.929-936).
Pseudojohannite from the Rovnost mine -
Image
At the La Creusaz U-deposit near Les Marécottes village, canton Valais, Western Alps, Switzerland,
pseudojohannite is directly associated with gypsum,
johannite, ktenasite,
marécottite and
uranopilite in a broader paragenesis that also contains
aluminium-bearing coconinoite,
jáchymovite, jarosite,
rabejacite,
schröckingerite, zippeite,
magnesiozippeite and
zeunerite. These minerals encrust blocks of
primary ore mainly consisting of
uraninite and quartz.
Pseudojohannite forms moss-green earthy aggregates up to 3 mm in size of poorly shaped crystals ~10 μm in
length.
Since the end of the underground exploration in 1981, out-cropping veins and stockpiled
uranium ore have been exposed to acid mine drainage water and atmospheric
oxygen in the abandoned galleries. The oxidation of the sulphides (mainly
pyrite and chalcopyrite)
resulted in the production of acid, sulphate-rich waters. These waters reacted with
uraninite, chamosite,
calcite and siderite to form a
rich assemblage of secondary
uranyl minerals, including pseudojohannite
(AM 91.929-936).
At the Widowmaker Mine, Fry Mesa, White Canyon Mining District, San Juan County, Utah, USA, pseudojohannite
is associated with coal, uraninite and
chalcocite
(HOM).
Pseudojohannite from the Widowmaker mine -
Image
Back to Minerals