Figure 3. Typical bedding in the rocks of the Perry Mountain Formation. This image shows light-colored quartzite layers with brown schist layers coupled in beds that are less than an inch to several inches thick. The light-colored knots in the schist layers are the metamorphic mineral andalusite. Although the layers in this image have all been exposed to the same metamorphic conditions, the andalusite is only found in the schist layers. Why is this? The parent materials for the schist were clay minerals rich in aluminum, a key component of andalusite. The quartz-rich layers were originally quartz sand which lacks aluminum, and thus will not support the development of andalusite and similar minerals regardless of metamorphic conditions.
Last updated on January 28, 2008