Calcite is a common rock-forming mineral with the chemical formula CaCO3 that is found throughout the world in sedimentary, metamorphic, and igneous rocks. It is the primary component of limestone and marble. Marl is a calcium carbonate-rich mudstone that contains variable amounts of clay and silt, with calcite being the dominant carbonate mineral in most marls. Migmatite is created when a metamorphic rock like gneiss partially melts and the melt recrystallizes, forming a mix of unmelted metamorphic and crystallized igneous parts, so it is classified as both a metamorphic and igneous rock.

5. Calcite is a rock-forming mineral
with a chemical formula of
CaCO3. It is extremely common
and found throughout the world
in sedimentary, metamorphic,
and igneous rocks. Some
geologists consider it to be a
"ubiquitous mineral“. Calcite is
the principal constituent of
limestone and marble.
Marl or marlstone is a calcium
carbonate or lime-rich mud or
mudstone which contains
variable amounts of clays and
silt. The dominant carbonate
mineral in most marls is calcite.
Therefore, it is classified as
either metamorphic, igneous or
sedimentary rock.
Migmatite is created when a
metamorphic rock, like
gneiss, partially melts, and
then that melt recrystallizes
into an igneous rock. This
creates a mix of an un-melted
metamorphic part with a
crystallized igneous part.
Therefore it is classified
under metamorphic and
igneous rocks.