Figure 3. This close-up shows thin nearly vertical layering. Directly beneath the eraser is a thin layer of schist. Just to the right of this is a thin layer of granofels, then another thin schist, followed by another thicker granofels layer. The overall purple color of the rock is a result of the large amount of biotite (a dark-colored mica mineral) in the rocks. Clay in the original sedimentary material was metamorphosed to biotite by heat and pressure.
Last updated on October 6, 2005