Which phrase describes foliated rocks?
A.tend to break in half
B.grains arranged randomly
C.tend to split apart along bands
D.grains arranged in increasing size
The Correct Answer and Explanation is:
The correct answer is C. tend to split apart along bands.
Explanation:
Foliated rocks are a type of metamorphic rock that exhibit a characteristic layered or banded appearance due to the alignment of mineral grains under high pressure and temperature conditions. This arrangement forms during the process of regional metamorphism, where rocks are subjected to significant pressure and temperature over large areas, such as at convergent plate boundaries or deep within the Earth’s crust.
In foliated rocks, the mineral grains (often composed of minerals like mica, chlorite, or biotite) align in parallel or subparallel layers, creating a foliated texture. This arrangement occurs because minerals with platy or elongated structures, like mica, tend to orient themselves perpendicularly to the direction of the applied pressure. As a result, foliated rocks break or split along these planes of alignment. These splitting planes are the characteristic “bands” of minerals that can be seen in rocks such as schist, slate, and phyllite. This feature is why foliated rocks tend to split apart along bands (Option C).
In contrast:
- Option A (“tend to break in half”) is not accurate for foliated rocks because they break along the aligned planes of weakness (bands), not randomly.
- Option B (“grains arranged randomly”) describes a non-foliated rock texture, where the mineral grains are not aligned in any particular direction. Non-foliated rocks, like marble and quartzite, do not exhibit the banded or layered appearance seen in foliated rocks.
- Option D (“grains arranged in increasing size”) does not describe the texture of foliated rocks. In foliated rocks, the mineral grain size can vary, but it is not typically arranged in a progressive size order.
Overall, the distinct property of foliated rocks is their ability to split along planes of alignment, making Option C the correct answer.