Hell's Canyon petrified wood. This rare wood, collected in the 1950s at a site now underwater at a dammed river on the Idaho / Oregon border, had dry rot and was compressed before petrification, creating its characteristic herringbone pattern.
It's funny that a lot of things I put into this category has to do with art. Art is just such a beautiful thing. It captures a moment that is so precious to the artist and expresses true feelings with swift movements that dance across the paper through shape form and line.