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13 February 2018
S-C fabric in limestone, Camerino, Italy
Some scaly Italian limestone shows off two foliations (S and C) which reveal the kinematic motions that built the Apennines.
9 August 2017
A suite of new 3D models
A showcase of five new 3D digital models of awesome rock samples and outcrops, produced using Agisoft Photoscan.
21 July 2017
Friday fold: Sardinia
My friend Ander Sundell at the College of Western Idaho is the source of today’s Friday fold. It’s from somewhere in Sardinia, and I think you’ll find it visually striking: Ander says: The rocks here are Silurian phyllites generated from mudstones that were deposited on the floor of the rheic ocean basin. The color and grain size variation do an excellent job highlighting compositional layering. They were deformed during the …
3 February 2017
Friday fold: Squaw Creek Schist, Idaho
The edge of ancestral North America can be found in the canyon of the Salmon River in western Idaho. Folds exposed the Squaw Creek Schist near Riggins record the stresses of adding terranes on during North America’s westward movement since the breakup of Pangaea. The Friday fold crinkled up during the accretion of a terrane to the growing North American continent.
25 November 2016
Friday fold: intrafolial folds in Eriboll mylonite
At the birthplace of the term “mylonite,” we can find Friday folds hidden in the foliation.
22 September 2016
Eyes on some augens in a nice gneiss
Take a look at these gorgeous exposures of augen gneiss in eastern “mainland” Shetland, U.K. Includes 3 GigaPans of the site.
12 September 2014
Friday fold: Quartz vein in Catoctin Formation, Point of Rocks, Maryland
I took this image in 2005, when I was working up a geologic history of the C&O Canal National Historical Park. It’s a vein of quartz, gracefully folded within the Catoctin Formation. The exposure is along the railroad tracks at Point of Rocks, Maryland, easternmost extent of the Blue Ridge province on the north shore of the Potomac River. The Culpeper Basin begins about 100 meters to the east of …
8 August 2014
Friday fold: Buckle vs. passive folding in the Chancellor Group slates
The Friday fold is an outcrop in Yoho National Park that showcases differences between buckle folding and passive folding.
10 May 2013
Friday fold: New Market / Lincolnshire formation contact, Staunton, Virginia
Happy Friday! Here’s a view of the folded contact between the (older, lower) New Market Formation, and the (younger, upper) Lincolnshire Formation, as exposed in Staunton, Virginia: The contact has been folded, pretty intensely: The New Market Formation is massive, light-colored, and exhibits fenestral texture here. The Lincolnshire is darker, more thinly-bedded, and is chock full of fossil invertebrates. Explore it for yourself in this M.A.G.I.C. GigaPan: link A closer …
29 April 2013
Kink bands in highly strained Laurel Formation, Rock Creek Shear Zone, DC
Last week before GSW, I spent several pollen-choked hours in Rock Creek Park, GigaPanning some of the rocks of the Rock Creek Shear Zone. Here are some exposures in the bed of Broad Branch that show lovely kink banding. In at least one spot, you can see a conjugate pair, so these rocks were (1) sheared out in a ductile shear zone, producing the foliation, and then (2) compressed under …
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.