Photomicrograph of an ultramylonite from the Pofadder shear zone in South Africa, a ~980 Ma dextral strike-slip fault exhumed from depths of 15 to 20 km.  The host rock is metagranite (?) This rock consists of a few small grains within a foliated matrix. This picture was taken under a magnification of 25X, under cross-polarized light.