The Caballos and Arkansas novaculite formations are thick, areally extensive cherts characterized by massive white "novaculite" chert. Field study of the formations shows common depositional features and highly variable bedding and coloration. Laboratory studies by petrographic, geochemical, X-ray, and electron-microscopic techniques show that the chert of these formations is composed of close-fitting quartz blocks 1-10 µ in size. Common small-scale depositional features, well-preserved siliceous fossils, and many beds containing dark sapropelic material are present.

The writers believe that the chert and novaculite formed from organically precipitated silica particles in the 1-10 µ size range. These particles accumulated below wave base where little detrital material was deposited and where current action was infrequent. In diagenesis, selective solution and redeposition on crystallization centers formed close-fitting blocks. The unusual thickness of siliceous rocks is partly due to the long time span (at least the Devonian Period) during which these formations were deposited.