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scorodite

Scorodite is a hydrated iron arsenate mineral with the chemical formula FeAsO4·2H2O. It forms as a secondary product in the oxidized zones of arsenic-bearing hydrothermal ore deposits and mine dumps. The mineral commonly occurs as blue to blue-green prismatic or tabular crystals, though it can also appear as earthy masses or crusts. It is relatively soft, with a Mohs hardness around 3.5–4, and it typically displays a vitreous to silky luster and a bluish color in well-formed crystals.

Formation and occurrence of scorodite are tied to the oxidation of arsenic-rich sulfide minerals such as arsenopyrite,

As a source of arsenic, scorodite is notable because roasting it yields arsenic trioxide (As2O3), historically

realgar,
and
orpiment
in
the
presence
of
iron
and
water.
It
often
accumulates
in
veins,
fissures,
and
on
mine
dumps
where
arsenic-bearing
minerals
weather.
Scorodite
has
been
reported
in
many
parts
of
the
world,
reflecting
widespread
arsenic
mineralization;
it
is
frequently
associated
with
other
arsenic
minerals
and
quartz.
used
in
the
manufacture
of
chemicals
and
pesticides
and,
in
some
contexts,
in
semiconductor
processing.
Because
scorodite
contains
toxic
arsenic,
handling
and
collection
should
be
done
with
appropriate
safety
precautions
to
avoid
inhalation
or
ingestion
of
dust.
The
mineral
is
of
interest
to
mineral
collectors
for
its
distinctive
blue
color
and
its
role
in
the
geochemical
cycling
of
arsenic.