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

Uploaded: 6 Apr 2020
Last Updated: 3 Jun 2020

368 megapixels
20,484 x 17,972 pixels
68.3 in X 59.9 in at 300dpi
5,844 pixels per inch

Or possibly Station Hills phyllite. Collected from a point bar in Accotink Creek, Fairfax, VA.