Pair of black and white Moroccan septaria

These Moroccan septarias have the particularity of revealing, once cut, magnificent black and white flames. This very contrasting pattern comes from a single node cut in half. For this reason we present them in pairs. They have been formed under the sea on layers rich in clay and it started with an organic remain (animal or vegetal) and the nodules were formed around it, with the wave agitation. But some anaerobic bacterias (able to live without oxygen, but producing ammonia), were trapped inside the nodule and kept developping. But ammonia, when in contact with sea water caused the precipitation of sulfates and carbonates. With time, the coats of clay become thicker and caused the suffocating of bacterias, and end of the nodule's growth. The carbonates, sulfates and sea water were saturated with Hydrogen sulfide and allowed shrinkage craks to form (that's a geode!) Later they have been coated by the precipitation of black and then white calcite: the flame that you see inside.