Quartz (Var: Chalcedony)
Glen Echo Ravine, Columbus, Franklin County, Ohio, USA
Dimensions: close up: 1.5" wide. Entire specimen: 5" x 4" x 2".
While opaque, matte, coarse-crystalline chert is the most common microcrystalline quartz found in concretions and nodules in the Ohio shale (and adjacent limestones), there are specimens that seem more characteristic of chalcedony: very fine crystals, semi-transparent, waxy, ...