Mineral Foundation Wissahickon schist is characterized by alternating layers of minerals, chiefly mica and quartz. Mica derives from the ancient shale, quartz from sandstone. A shiny, flaky mineral, mica gives the schist its glassy or metallic appearance. Quartz is often chalky white or clear, though it may also occur in smoky blue, gray, or other shades. Whatever its hue, quartz is hard - it can scratch the surface of a coin.
Children especially enjoy scouting for the embedded garnets.
The characteristics of the minerals influence the rock as a whole. For instance, because of its molecular structure, mica has cleavage, a tendency to fracture along planes. For this reason, the Wissahickon schist also tends to split into thin layers, parallel to the cleavage of the mica. In addition, the many fractures in the schist provide seepage outlets for groundwater - hence the large number of springs in the park. In contrast to mica, quartz has no cleavage and is very difficult to break.