1 minute read
Schist
by AudioLearn
SCHIST
Figure 43.
Advertisement
Schist is more fine-grained with a lot of foliation. Schist essentially means split in German. Shale is the preexisting rock that then gets folded and compressed to become mica. When you see the shiny mica fragments, you can expect this to be schist. The rest of the rock often comes from shale so it will be relatively dark gray in color. Other schists come from hornblende and quartz.
Schist has much larger granules and you will see the parallel layers fairly well. These greatly vary with regard to their color and texture. You would call a rock having a schistose structure if it has a schist-like appearance. Look for lines and micas of both kinds; there are many other minerals possible, including hornblende and chlorite.
Mica schist is extremely common, having fine sediment made from plagioclase, biotite, muscovite mica, and occasionally garnet. Others, like hornblende schists, come from basalt with quartz, plagioclase, and hornblende in them. Figure 44 is mica schist:
Figure 44.
Two groups of schists can be seen. Low grade schists involve low temperatures leading to minerals like muscovite, chlorite, and albite. These are unstable at higher temperatures. Mica-schist is a good example of this. High-grade schists come from mineral-rich areas to give rise to stable minerals like garnet, andalusite, and cordierite. Cordierite is purple or lavender and looks like this image in figure 45:
