Geo 730: March 6, Day 430: Dendrites I

Most of the jointing surfaces in the platy lava at the Doherty Grade pull out show nicely developed dendrites. These are generally precipitates of slightly mobile/soluble metallic oxides/hydroxides, not, as they might appear to the geologically naive, actual fossils. My baseline assumption is that manganese oxide is the dominant component, though I read maybe 10 or 15 years ago that most of the time it's not pyrolusite, which was my assumption up until that point. If I recall, it's compositionally equivalent to that mineral, but amorphous. While quite apparent at the above scale, the variety of forms is best appreciated in the full-size version of the photo (right click and select "open link in new tab").

Photo unmodified. August 19, 2011. FlashEarth Location.