Sibley rock display: autoclastic basaltic breccia

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Sibley's rock collection: autoclastic basaltic breccia

Autoclastic basaltic breccia
Autoclastic basaltic breccia:
Dike rock that ground itself up while injecting into understory of the volcano

This rock is displayed in “Sibley's Geological Treasures” collection on the roofed patio of the visitor center in the Robert Sibley Volcanic Regional Preserve. The above caption is the same that is given on-site (June 11, 2012).

Autoclastic basaltic breccia is a rock composed of fragments of basalt and other rocks cemented together. The fragments formed in place by grinding of dike rock (tabular or sheetlike body of igneous rock).