Up close you will see this specimen is (or was) loaded with small tabular Wulfenite crystals. They are now covered with green Mottramite. Ex. Paul Nicholson collection with tag.
Mottramite
Formula
PbCuVO4(OH)
Crystal System
Orthorhombic
Crystal Habit
Plumose, Radial, Encrustations
Cleavage
None, None, None
Luster
Greasy (Oily)
Color
brown, brown red, brownish black, green, dark green