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cancrinite

Cancrinite is a rare alkali feldspathoid mineral that belongs to the cancrinite group. It is a complex sodium-calcium carbonate-silicate and typically forms in alkaline igneous rocks and carbonatites. The mineral contains carbonate (CO3) groups and silicate (SiO4) tetrahedra, with sodium and calcium as major cations; some samples may exhibit fluoride substitutions, giving rise to related species such as fluorcancrinite.

In terms of crystallography, cancrinite crystallizes in the hexagonal system and commonly occurs as prismatic to

Geologically, cancrinite forms in a variety of alkaline settings, particularly in nephelinite, phonolite, and carbonatite networks.

Fluorcancrinite, a fluorine-rich variety, and other related members occur in similar environments, illustrating the chemical flexibility

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tabular
crystals,
as
well
as
granular
masses.
Its
color
ranges
from
yellow
to
orange-brown,
with
rare
blue
or
greenish
tints.
It
has
a
vitreous
luster
and
is
transparent
to
translucent.
On
the
Mohs
scale,
its
hardness
is
about
5.0
to
5.5,
and
its
specific
gravity
is
approximately
2.2
to
2.4.
Cleavage
is
poor
or
indistinct,
and
fractures
are
conchoidal.
It
is
commonly
found
in
cavities
and
veins
within
these
rocks
and
often
occurs
alongside
other
feldspathoids
such
as
natrolite
and
nepheline,
as
well
as
carbonate
minerals
like
calcite
and
fluorite.
The
mineral
is
also
of
interest
to
collectors
due
to
its
rarity
and
the
sometimes
striking
coloration
of
its
crystals.
of
feldspathoid
minerals
in
alkaline
systems.