By: magic-gigapans
Image: Callan Bentley, Mid-Atlantic Geo-Image Collection
License: Creative Commons Non Commercial ⧉

Uploaded: 14 Apr 2020
Last Updated: 29 May 2020

881 megapixels
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Lower Devonian limestone of the Graz Paleozoic section of the Noric Nappe (Upper Austro-Alpine) approximate location: 47° 12’ 45” N 15° 20’ 37”E. The crystals are pyritohedrons not framboids, therefore as they rotate, fibers suddenly start growing from a new face cause “fiber unconformities” (not great in this particular specimen, though). Students may wonder why the crystals are often at one end of the fiber, not symmetrically in the middle. It’s an excellent quiz question. The smartest students will conclude that there is an oppositely asymmetric fiber on the rock that was broken off to reveal this face. Sample from the structural geology collection of Carol Simpson and Declan De Paor.