Joint- and bedding-bound cube of radiolarian chert, Peloponessos, Greece

The upper and lower planar surfaces are bedding planes. The other facets are joint faces. The thin layers of radiolarian chert were systematically jointed during compressional deformation. What makes this specimen unique is that there are two directions of jointing at right angles to one another, with joint spacings the same as layer thickness. As a result, weathering and erosion can create perfect cubes in outcrop.

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 find the shape appealing, calling attention to Bruno Sander’s emphasis that the symmetry of deformation reflects the symmetry of applied forces.  Moreover, were you to hold this rock in your hand, you would think it was made of cardboard or balsam wood.  It is very light.  The rock was deposited in a sediment starved basin very far from shore, and the only things that were deposited were shells (tests) of tiny pelagic organism which would die near the surface of the sea, and then ‘rain’ down kilometers to the deep bottom.  Thus the ‘rock’ is made of ‘hollow’ shells, i.e., much porosity.

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