Final answer:
The material between cleavage planes that exhibits folding, kinking, or flattening is associated with foliated metamorphic rocks. Thin layers of mica and thick layers of quartz, feldspar, and mica are examples. Cleavage must be identified to understand a rock's geologic history.
Step-by-step explanation:
The material between cleavage planes that is folded, kinked, or flattened, is typically mineral layers found within metamorphic rocks. These rocks may exhibit features such as very thin layers, wavy layers with a sheen, thin layers of mica, or thick layers consisting of quartz, feldspar, and mica. The term foliation describes the planar arrangement of structural or textural features in metamorphic rocks along straight or wavy planes. Recognizing cleavage is crucial for identifying minerals within rocks, which can then reveal information about the rock's geologic history.
In order to identify cleavage in minerals, it is often helpful to shine a light on the surface of a mineral to see if it brilliantly reflects light, indicating the presence of a cleavage plane. Non-foliated metamorphic rocks, in contrast, tend to be massive and structureless at a glance, with mineral crystals growing in many directions without showing alignment.