13.9: Other Metamorphic Rocks

Other Metamorphic Rocks

If a metamorphic rock is heated enough, it can begin to undergo partial melting in the same way that igneous rocks do. The more felsic minerals (feldspar, quartz) melt, while the more mafic minerals (biotite, hornblende) do not. When the melt crystallizes again, the result is light-colored igneous rock interspersed with dark-colored metamorphic rock.  This mixed rock is called migmatite Links to an external site. (Figure 13.20, left and left center).

Metaconglomerate Links to an external site. (Figure 13.20, right center) looks similar to conglomerate, although sometimes the clasts are deformed (stretched or elongated). The original cement has recrystallized and may be quite durable. Some metaconglomerates may exhibit weak foliation, forming similar to slate or phyllite.

Hornfels Links to an external site. (Figure 13.20, right) is a fine-grained non-foliated metamorphic rock with no specific composition, although it commonly forms from the protolith shale or mudrock. It is typically produced via contact metamorphic in the metamorphic aureole.