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Point Bonita metabasalt pillows, Bay Area, California

By California Volcano Observatory
Looking down from a cliff into the sea, a crag of stacked black pillows of volcanic rock rises from the rough surf. Some of the pillows have a greenish tinge.
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Detailed Description

In this view down from the Point Bonita lighthouse, a sea arch made up of slightly metamorphosed pillow basalts rises from the surf. The green tinge on some of the "pillows" is the result of metamorphism, replacing primary minerals with greener ones such as chlorite and epidote. USGS photo by Jessica L. Ball

Sources/Usage

Public Domain.