On the eve of Opportunity's landing to investigate hematite at Meridiani Planum, I though it might be appropriate to post some images I took this summer while digging dinosaurs.

The badlands of central Montana, near Fort Peck reservoir are an excellent place for dinosaur paleontology. There are exposed millions of years of "soft" sediment from the entire cretaceous period with plenty from adjacent periods. Here it's possible to efficiently discover new dinosaur specimens by walking around and looking for exposed bones in the appropriate layers. As there are bones everywhere exposed in the layers, the trick is to look for whole bones that are associated with nearby whole bones so as to discover an articulated and nearly complete specimen. Then the diggers move in and remove the overlying dirt or overburden back into the formation. They then descend slowly into the formation with scrapers and brushes so as not to destroy the bones and to record their relative positions. This was the site known as F-rex.

(f-rex picture)

The F-rex site is named after Frank a friend of Homer Hickam who has discovered some sites of his own out here. They prospect on a volunteer basis for a few weeks as a kind of vacation during the field season. This site was fractured mudstone which is nice to remove as overburden as large chunks come off easily, but is a pain in the butt to scrape through. I said the site was called F-rex because we never found any specimen to speak of. What I did notice was that as we removed the overburden, a large piece of mudstone came off the back wall intact and revealed the face of a rather large fracture with a wonderland of hematite pigment.

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Inserted for scale is my large sized and embarresingly shiny "physics" rock hammer. I say this as it is apparently a virtue for geologists-paleontologists and the like to have a well weathered hammer. I still intend to install avionics in mine and to keep it shiny as the day it was new. PPPbbbtthhhh!!! ;) Just above the hammer's head, you can see the jackhammer marks from prying the big chunk away from the formation. This is what the underlying mudstone looks like. The hematite is just a colorful pigment on the surface.

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Here is a closeup of a fractured area that shows well the contrast between the two colors of hematite found in the picture. The blue and red reflect the thickness of the hematite coating on the mudstone. The red region is where there is incomplete and thin coating of the surface on a micron scale. Here it interacts with light more like a particle.

As the coating grows thick enough so that the particles "grow" together, it then takes on more of it's crystaline properties where it strongly absorbs red and looks blue or purple. This is also the form that is known as grey hematite, I think.

This is such a great picture because the continuous transition from red to blue can be seen in some areas. The contrast at the fracture also clearly shows that the fracture was probably a conduit for iron rich water that deposited hematite below the fracture.

This last picture is still a bit of a mystery to me. Down is to the right.
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The ovoid objects are gypsum (calcium sulfate) crystals, which can be found all over the area in various granularity. Everything from a fine white powder to large sheets of cm crossecton scepters. Here we see crystals that were nucleated and grew in the fracture space. Beneath them are tracts where presumably water interacted with the gypsum, became acidic and etched the coating of hematite from the rock. I'm just guessing it was acidic because of the sulfate-sulfuric acid connection, if anyone knows the particulars of this please enlighten. On of the geochemical minded folks that I asked about the ubiquity of the gypsum said it probably had to do with the nature of the formation itself. Apparently, this entire formation is mostly the result of ashfall and modification from volcanism at upwind plate boundaries. A recent example of this is Mt. St. Helens which bumped a large abount of ash on Montana in 1981. Volcanic ash is relatively high in sulfur, chlorine and other nasty volatiles.

Ok, that was fun. Now, go Opportunity!!