16 August 2010

How to prep your pocket fold

Posted by Callan Bentley

“Pocket folds,” as my Rockies co-instructor Pete Berquist has defined them, are rock samples exhibiting folds that are small enough to stick in your pocket (and take back to your lab). Here’s a pocket fold that I found last week in the White Mountains of New Hampshire:

I brought it home, and today I unpacked it from the car, along with about 70 pounds of other samples. I turned on the hot water tap and took out a critical piece of sample prep equipment, the wire brush (suitable for cleaning a grill), and scrubbed off all the algae. You should only use wire brushes on relatively hard samples. Because the steel wires have a hardness of 5.5, they will scratch rocks like limestone, which is made of 3.0-hardness calcite. I also gave it a quick bath in 4.5 molar HCl, to kill off any remaining algae. A rinse, and then I set it in the sun to dry.

My White Mountain pocket fold is a quartzite, with some nice graded beds, which probably show up better when they are filled in with algae. Regardless, here’s the cleaned up sample, a gray ghost of a pocket fold:

If you collect field samples for teaching purposes or just because you find them beautiful, what steps do you take to prepare them?