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5 June 2012
A clutch of amygdules
Callan presents a collection of well-exposed amygdules, seen along the Dark Hollow Falls trail in Shenandoah National Park, Virginia. These white dots on a green background are the signatures of (1) Iapetan rifting, and (2) Alleghanian metamorphism.
15 May 2012
Diabase dike in diabase
Seen in rip-rap on the side of Naked Creek, a week ago yesterday: This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).
11 April 2012
Blue Ridge Thrust Fault field trip
One of Callan’s former students leads a field trip to examine the western edge of the Blue Ridge geologic province, attempting to answer the question of whether the Blue Ridge / Valley & Ridge contact is indeed the trace of a thrust fault. Breccias and S-C fabrics tell part of the story…
5 April 2012
Red Bluff Granite, and what it intruded into
Returning to his February field trip in west Texas, Callan examines the contact zone where the Red Bluff Granite intruded into a group of surficial rocks, including columnar-jointed basalt.
2 April 2012
Castner Marble
The Castner Marble is an extraordinary Mesoproterozoic limestone (later re-crystallized and metamorphosed) that exhibits some primary structures (both explicit and ambiguous) and some secondary (tectonic) overprints. It’s exposed in the Franklin Mountains of west Texas.
28 March 2012
Hanksite and other wonders of Searles Lake
Callan’s field studies class journeys to Searles Lake, California, a playa rich in evaporite minerals both prosaic and exotic.
10 February 2012
Cuprified wood
This is insane. Check it out – a malachitized and azuritized log, on display in front of the Geological Sciences building at the University of Texas at El Paso: Have you ever seen anything like that? It’s cool meets cool. Awesome.
21 January 2012
Turkish blueschist macro-GigaPan
With my new “macrogigapan” rig from Four Chambers Studio, I produced a single image last week as part of my Mid-Atlantic Geo-Image Collection project (M.A.G.I.C.). I’m still learning the ropes of the machine – I shot about 3 times as many photos as I needed to to make this gigapan. Lessons learned, yet again. Anyhow … Dive in! You can make it full screen by clicking on the ‘GigaPan’ logo …
22 December 2011
Virtual sample gigapan #1: pyrolusite dendrites on limestone
With my new “macrogigapan” rig from Four Chambers Studio, I produced this image last week before I left on vacation: That sample measures 18.5 cm long, and is about 4.9 cm wide. Pretty good resolution, eh?
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.