Two Occurrences of Shatter-Cone-Like Fractures
Fractured surfaces almost morphologically identical to shatter cones were found in museum specimens of Cambrian shales from two widely different localities: (1) in the Mojave Desert, California (34°35′ N., 115°30′ W.), and (2) in the Avalon Peninsula, Newfoundland (47°32′ N., 52°57′ W.). The cones differ significantly from cone-in-cone, and their observed features do not suggest an organic origin. The cones are very rare in the California locality and no other features that could be interpreted as shock-induced were observed during a recent field visit. The Newfoundland locality has not been re-examined. Evidently shatter-cone-like fractures may be produced in shales by processes unrelated to shock waves.