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

Uploaded: 17 Apr 2020
Last Updated: 3 Jun 2020

799 megapixels
32,250 x 24,786 pixels
107.5 in X 82.6 in at 300dpi
6,883 pixels per inch

This rounded cobble (gravel from the shores of one of the ancient glacial lakes that once filled the valley of Glen Roy) shows porphyroblasts of different metamorphic minerals in different horizons - probably correlating to compositional variations in the sedimentary protolith. What are the minerals? How could you use these minerals to constrain the composition of the original sedimentary strata? What sorts of pressure/temperature constraints can you place on this rock's metamorphic history? Obverse of this sample: https://viewer.gigamacro.com/view/hA4ovbu4voFcM7iS