|Photo by Mrs. Geotripper|
|Geotripper checks out a really cool outcrop (photo by Mrs. Geotripper)|
|The Monterey Shale is usually white; why is it gray here?|
So what was the mystery rock? I was educated as a geologist, not a teacher, so it took a few years before I heard about the concept of discrepant events in education. A Discrepant Event is something that "surprises, startles, puzzles, or astonishes the observer. Often, a discrepant event is one that does not appear to follow basic "rules of nature" and the outcome of a discrepant event is unexpected or contrary to what one would have predicted". Well, Tuesday's mystery rock wasn't a discrepant "event", it was a discrepant outcrop. The result looks like something familiar, but is far from normal.
I suggested that readers follow their intuition, and that their answers would be "sort of half right". Most respondents suggested that they were looking at obsidian (above), and some kind of tuff or scoria (below). They were sort of half right. The problem is that these rocks are not volcanic at all. Brian, at my Google+ page maybe came the closest by guessing that these were fulgerites, fused rocks caused by a lightning strike.
So, is this rock igneous, sedimentary or metamorphic? Some sources refer to combustion metamorphism, others refer to fused shale. No one talks about magma. In any case, I found the rock fascinating. Even downright sexy.
More information on this cool outcrop can found here. It is located on Grimes Canyon Road just a few miles south of Fillmore, California.