A. The layer in the center has needles of the black mineral hornblende which grew in a white rock composed of the mineral plagioclase. Neighboring layers are dominated by these same two minerals, but in different proportions, giving a striped or layered appearance. Rocks of this composition were probably volcanic rocks before the metamorphism.
B. This rock has patches and streaks of a pale apple-green mineral (diopside) and a cinnamon-brown mineral (garnet), which grew in response to heat during metamorphism. These minerals have compositions which indicate the rock has a relatively high content of calcium and silica, and was probably derived from a sandy limestone (or limy sandstone).
C. White pebble-shaped rocks may have been fragments ejected during a volcanic eruption during the initial formation of the rocks. The high degree of subsequent metamorphism has undoubtedly distorted them, making it difficult to know their origins with certainty. Other interpretations are possible.
