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Celestite

Celestite, or celestine, is a mineral composed of strontium sulfate (SrSO4). It commonly occurs as well-formed crystals in sedimentary rocks, especially evaporite deposits, and is often found alongside gypsum and other sulfates. The name derives from the Latin caelestis, meaning heavenly, in reference to its usually pale blue color.

Crystals of celestite are typically orthorhombic and may be prismatic or tabular. The mineral is usually transparent

Celestite forms in sedimentary environments where evaporites concentrate, filling voids and cavities in limestones and shales.

to
translucent
with
a
vitreous
luster
and
a
color
range
from
pale
blue
to
colorless,
with
occasional
pink
or
gray
tints.
It
has
a
Mohs
hardness
of
3
to
3.5
and
a
relatively
high
specific
gravity
around
3.96.
It
is
commonly
associated
with
gypsum,
anhydrite,
halite,
and
other
sulfate
minerals.
The
mineral
is
mined
as
an
ore
of
strontium
and
is
an
important
source
of
strontium
compounds
used
in
fireworks,
glassmaking,
and
ceramics.
In
addition
to
its
industrial
applications,
celestite
is
valued
by
mineral
collectors
for
its
delicate
blue
crystals
and
is
sometimes
used
as
an
ornamental
stone.