Pie wedge of bedding- and joint-bounded radiolarian chert, Peloponessos, Greece

The upper and lower planar surfaces are bedding planes. The other facets are joint faces. Joint faces are complete, with a main joint face feathering into a shoulder of fringe jointing, where tiny fractures are twisted into en echelon joints that are not strictly parallel to the overall main face. As the propagating joint looses energy, the direction of greatest tension shifts slightly, and this is reflected in the change in joint orientation.

I collected this rock during the summer of 2004 in the Pindos fold and thrust belt of the Peloponessos near the village of Ano Karyes.  I like the fact that the fringe shoulder of the main joint face is so obvious, and thus the joint morphology is so complete.  Moreover, the color reminds me of fudge. 

Age & Formation
Radiolarian chert from within Chert Series Beds of Jurassic age, ~180 Ma, Peloponessus, Greece