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porphyroblastic

Porphyroblastic is a texture term used in metamorphic petrology to describe rocks that contain conspicuously large crystals, called porphyroblasts, embedded in a finer-grained groundmass. The presence of such oversized crystals gives the rock a distinctive, porphyroblastic appearance.

A porphyroblast forms and grows during metamorphism when conditions such as temperature, pressure, and chemical environment

Common porphyroblasts include garnet, staurolite, kyanite, sillimanite, cordierite, and other minerals that crystallize under specific metamorphic

Significance lies in using porphyroblasts to interpret metamorphic histories. Zoning within porphyroblasts can record changes in

favor
the
crystallization
of
a
mineral
to
a
size
larger
than
surrounding
grains.
The
matrix
may
consist
of
minerals
that
crystallized
earlier
or
later,
and
porphyroblasts
can
overgrow,
separate
from,
or
react
with
the
surrounding
material.
Growth
rims
and
inclusion
patterns
within
porphyroblasts
provide
clues
to
their
history
and
the
sequence
of
metamorphic
events.
conditions.
The
type
and
abundance
of
porphyroblasts,
as
well
as
their
zoning
and
inclusion
textures,
help
indicate
metamorphic
grade
and
the
pressure–temperature
path
of
the
rock.
Porphyroblasts
may
also
be
surrounded
by
corona
textures,
formed
when
the
surrounding
matrix
reacts
to
the
growth
of
the
porphyroblast.
PT
conditions
over
time,
and
the
composition
of
inclusions
can
reveal
prior
mineral
assemblages.
Thus,
porphyroblastic
textures
are
a
key
feature
for
reconstructing
PT
paths
and
metamorphic
evolution
in
regional
and
contact
metamorphic
terrains.