Sibley rock display: basaltic breccia with limestone matrix

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Sibley's rock collection: basaltic breccia with limestone matrix

Basaltic breccia with limestone matrix:
basaltic fragments thrown into air, landed in pond water inside volcano,
and settled into calcacerous mud

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).

Basaltic breccia is a rock composed of fragments of basalt and other rocks cemented together.

Breccias are found in the Berkeley Hills including the preserve's Round Top, which was once the infilling of a crater.