2 November 2010
Posted by Callan Bentley
Obsidian bearing well-developed conchoidal (clam-shell-shaped) fracture with concentric ribs, as displayed at the recent U.S. Science and Engineering Festival on the National Mall by a local gem/fossil/mineral club.
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
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i am learning about conchoidal fractures now. The are beautiful. I wish I could find an explanation for them that is made for beginners and easy to understand.
Thanks for the great photo!
p.s. I am glad your fingernails were clean!lol
You strike the lithic with an object, preferably another rock.