Outside the Interzone
Outside the Interzone 's Latest Posts
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 […]
One last shot of the platy jointing on Doherty grade- there will be a few more shots of hand samples, most with another feature of interest, but this is the last of the outcrop scale examples. The reason I've spent so much time on this is simple: the things that particularly capture my attention are things that are rare, or inexplicable- to me, at least. It wouldn't surprise me if there is a good explanation for how this structure forms, but I don't know what it is. And when I try to think […]
More platy jointing, and Dana examining a rubbly portion of the flow(s). As I recall, there were some area of secondary mineralization, with agate and calcite, in the rubbly parts. Dana was quite taken with that, though in my opinion, it didn't even begin to compare with what we found at the next stop... we'll be getting to that one in a week or so.Photo unmodified. August 19, 2011. FlashEarth Location.
A closer view of the same shot as yesterday. While the platy flows seem to dominate here, there are other flows as well. To the right and below the hammer, there's a rubbly, red, scoria-like flow; a similar one is visible in the upper left of yesterday's photo. These may actually be a part of the same flow as the platy material, representing the basal and surficial breccias, equivalent to aa-aa. I'm not at all certain about that, as the rubbly lava is much more vesicular than the platy lava, […]
Platy jointing along Doherty Grade. Hammer in lower center for scale. As I mentioned two or three days ago, I'm not sure what kind of rock this is; it's too fine grained to get any sense of mineralogy. On a stop here with Anita Grunder, a volcanologist with OSU, she assessed it as basalt. She's certainly much more qualified and experienced than I am in these matters, but I'm not convinced. There's something about the way it rings that just isn't "basalt-like." It seems to me it's too felsic for […]
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