f019253d_The_Delaware_Geological_Survey_inerals_of_the_Red_Clay_Valley_Description
[Rock Type] Pryoxene [Description] 
A group of dark minerals that are common in the Piedmont rocks. They usually occur as interlocking grains in the highest-grade gneisses, amphibolites, and gabbros.
Common Rocks and Minerals of the Delaware Piedmont | The Delaware Geological Survey
Description