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Cordierite Hornfels

Detailed Description

Hornfels rocks are metamorphic rocks. They usually start out as sedimentary rocks like sandstone or shale, but then volcanic material pushes up from below and bakes the sedimentary rock into a metamorphic one. Hornfels are known for being exceptionally tough and durable. This one is from Chantilly, VA.

Sources/Usage

Public Domain.