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autunite

Autunite is a hydrated calcium uranyl phosphate mineral with the formula Ca(UO2)2(PO4)2·10–12H2O. It belongs to the autunite group, which includes minerals sharing the uranyl phosphate framework but differing in hydration and cation content (for example, torbernite with copper and meta-autunite with lower hydration). Autunite forms as a secondary mineral in the oxidation zones of uranium-bearing deposits and in granitic pegmatites.

The mineral commonly appears as yellow to yellow-green tabular crystals, though it also occurs as crusts or

Autunite fluoresces bright yellow-green under ultraviolet light, a feature shared by many uranyl minerals. Its hydration

Named for Autun, France, the type locality of the mineral, autunite is now found in uranium-bearing districts

staining
on
fracture
surfaces.
Crystals
are
often
platy
or
blade-like
and
may
aggregate
in
radiating
groups.
It
has
a
vitreous
to
resinous
luster
and
a
color
range
from
pale
to
olive-yellow.
Autunite
has
a
Mohs
hardness
near
3,
making
it
relatively
soft,
and
it
is
radioactive
due
to
its
uranium
content,
requiring
caution
in
handling
and
storage.
level
is
variable;
dehydration
yields
meta-autunite
and
other
phases,
reflecting
a
dynamic
hydration-dehydration
equilibrium
in
natural
environments.
around
the
world.
It
commonly
occurs
with
other
uranyl
phosphates
and
uranium
oxides
and
is
of
interest
to
mineral
collectors,
geologists
studying
ore-forming
processes,
and
collectors
of
radioactive
minerals.