Chopawamsic Gneiss


Complexly deformed gneiss in the Chopawamsic terrane near Cuckoo, Louisa County. Photo by C.M. Bailey

This exposure in a pasture near Cuckoo exposes a poly-deformed hornblende and plagioclase-rich gneiss. Foliation in the gneiss has been refolded.  Another interesting feature is the presence of garbenschiefer or “feather amphibolite.” This unusual texture is defined by stellate and featherlike hornblende clusters in the plane of foliation. Three amphibole species occur in this rock with hornblende and cummingtonite dominating the mafic layers and actinolite, as a late stage mineral overprinting the earlier fabric. The two-stage amphibole growth is evidence for two phases of metamorphism.


Close up view of stellate hornblendes forming garbenschiefer.