Which metamorphic rocks have banded layers?

Which metamorphic rocks have banded layers?

• A. Foliated
• B. Non-Foliated
• C. Sedimentary
• D. Igneous

Answer: (A)

Banding in metamorphic rocks is called foliation. This occurs when rock is subjected to directed pressure during metamorphism, causing minerals to realign into parallel planes. The alignment of platy minerals, like mica, creates visible layers that run in a consistent direction, producing the characteristic banded appearance. Rocks such as slate, with its fine foliation; schist, with more pronounced mineral sheets; and gneiss, which shows alternating light and dark mineral bands, are classic examples of foliated metamorphic rocks. Rocks that don’t show this layered texture are non-foliated metamorphic rocks. They form under heat or pressure that is more uniform, so their minerals recrystallize without a preferred orientation, resulting in a more uniform look (for example, marble or quartzite). Sedimentary rocks may display bedding from sediment deposition, and igneous rocks have interlocking crystals, but neither category is defined by the banded, directed-pressure foliation seen in foliated metamorphic rocks.

Banding in metamorphic rocks is called foliation. This occurs when rock is subjected to directed pressure during metamorphism, causing minerals to realign into parallel planes. The alignment of platy minerals, like mica, creates visible layers that run in a consistent direction, producing the characteristic banded appearance. Rocks such as slate, with its fine foliation; schist, with more pronounced mineral sheets; and gneiss, which shows alternating light and dark mineral bands, are classic examples of foliated metamorphic rocks.

Rocks that don’t show this layered texture are non-foliated metamorphic rocks. They form under heat or pressure that is more uniform, so their minerals recrystallize without a preferred orientation, resulting in a more uniform look (for example, marble or quartzite). Sedimentary rocks may display bedding from sediment deposition, and igneous rocks have interlocking crystals, but neither category is defined by the banded, directed-pressure foliation seen in foliated metamorphic rocks.