[MSA-talk] Percussion marks

Clemens, JD, Prof <jclemens@sun.ac.za> jclemens at sun.ac.za
Tue Dec 19 15:21:33 EST 2017

I guess Ap could be deformable enough to locally warp the lattice. Then, the difference in orientation of the warped lattice and the underlying less-deformed structure could create an internal diffraction wedge. You see this in cracked crystals, where the wedge is filled by air. Is that what’s going on?

Prof. John D. Clemens
Dept of Earth Sciences
University of Stellenbosch
+27 (0)21 808 3159

On 19 Dec 2017, at 20:16, Chris Tacker <rctacker at yahoo.com<mailto:rctacker at yahoo.com>> wrote:

Hello, all,

Is there a term to describe the fringes that form around a percussion mark? Attached is a photo of an apatite,
not quite before and after, but it clearly shows color fringes in cross-polarized light. The crystal is about 1 cm, and it was simply poked with a phillips head screwdriver to make the mark.

Chris Tacker
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