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Megacryst
In
geology
, a
megacryst
is a
crystal
or
grain
that is considerably larger than the encircling
matrix
. They are found in
igneous
and
metamorphic rocks
. Megacrysts can be further
classified
based on the
nature
of their
origin
, either as:
Phenocrysts, which
crystallize
in
molten rock
material
and are
hence
an earlier
crystallization
than
the matrix
in which they are
embedded
Porphyroblasts, which
develop
in
solid
rock
as the result of
metamorphism
or
metasomatism
