Were I boots-on-the-ground there, the second thing I'd do is kick it or thwack it with a hammer. Scuffing the soil with one's boot-toe is a time-honored tradition.

--Bill

That stereography was very informative. With the 3D we can clearly see that the lineations that are apparent crossing the top surface of the Homestake are actually "planar" surfaces extending down into Homestake on an angle. I'm not sure what to make of these surfaces. I suppose they could be faces of individual crystals comprising the "vein," or perhaps compositional banding.

Indeed. And these are not even particularly good quality images. The exposure-- or histogram stretching routine-- is set for an average value of the dark-toned background and almost pushes the light-toned vein material almost through the ceiling. They will no doubt tweak the exposure a bit, and the range quirk will be resolved when the images reach the PDS. All we see now are hints of the full texture.

Today's (Sol-2766) AM images show that the three fragments in the upper side of the vein have a crystalline texture:

http://qt.exploratorium.edu/mars/opportuni...27P2905M2M1.JPG

http://qt.exploratorium.edu/mars/opportuni...27P2905M2M1.JPG

There are 15 MIs of 3 "poses" on tap for transmission today, so we can look forward...

--Bill

Doesn't a vein like that require some long-ago sedimentation process involving liquids?

Precisely, Dr. Watson.

Not sedimentation-- that implies transport and deposition of particles (like sand or silt) by a fluid (like water) in a stream. What we have here is the deposition (crystallization out of a saturated solution) of minerals from a fluid (like water) in a fracture. Called a fracture fill in general terms and is a hydrothermal (and specifically cold-water hydrothermal) process. I'm picking nits, to be sure, but to a geeeologist these are specific and different terms, and we're talking about geology here.

You've heard me babble and talk-in-tongues about this before. This is a major find. By determining the specific types of minerals present here, we can intuit the exact environmental conditions present at the time of their creation.

This is like that erratic we found a couple of years ago, Marquette, that turned out to be a piece of gabbro (peridotite) ejecta that appeared to may have undergone serpentization (a hydrothermal process, alteration, weathering). Sorry, there are a few things in the universe that will make a geologist go bonkers, and this be one of them...


--Bill

And, just stating the obvious, the fact that Homestake sticks up tells us two things:

1) It is more resistant to erosion than the host rock
2) An unknown, but possibly substantial thickness of host rock and vein has been removed by erosion

Googling for images of "resistant vein outcrop" reveals some similar features on earth. If you don't include the word "outcrop" you'll see veins of a different kind.

And on the terminology theme, rather than "sedimentation" it might be more accurate to say the vein mineral(s) precipitated from a hydrothermal fluid.

Bill beat me to it, but I just wanted to add a couple of minor points. Veins are very often created by the precipitation of minerals from liquid solutions, but liquids are not always required. They can be formed by deposition from a vapor as well, so it might be more accurate to say fluid rather than liquid. Furthermore, deposition or precipitation need not necessarily be involved, as a fluid moving through a fracture in rocks can also replace existing mineral in the wall rocks with new minerals.

edit: I just remembered yet another process. Veins can also be formed by the direct injection of magmatic material into country rock.

And here is an image of the rock Yates on Sol-2765. Yates is in the Meridiani-Endeavour onlap zone adjacent to Homestake and hopefully will be one of the areas of study during the winter stopover.

--Bill

Another messed about with portrait of Homestake...

Since we have a full set of right filter images of Homestake from sol 2765, I thought I would make a false color, infrared ratio, hematite signature image (hematite should appear as yellow). It doesn't tell us what Homestake's mineralogy is, but it does tell us that the vein is not composed of hematite.

It is also interesting to note that there are several spherical pebbles in the left center portion of the image that have the yellow hematite signature, as we had previously seen.

My big fear (apprehension, really) is that the vein will turn out to be calcite. That would truly send our house of cards crashing down! Almost as bad would be quartz, which "shouldn't be" in a Mafic regime like this. It'll be significant, whatever it is.

--Bill

Calcite has a Mohs hardness of 3. Wouldn't that be to soft for this environment?
The way the vein sticks up from the parent rock, it appears harder then that.

Quartz is what it looked like at first glance to me but as Bill said it shouldn't be in a mafic setting i think granitic settings are where it usually lives but granite is rare on Mars so yes it would very interesting if that is what it is. (Quartz needs lots of reworking of rocks I think)
Roy

With the calcite it's not a question of physical hardness, it's that under acid (non-neutral) conditions calcium and bicarbonate won't make the carbonate. However, other carbonates are more possible-- the series of magnesium-iron carbonates (magnesite->siderite) are common around mafic rocks, so the basic recipe is there. No matter what, the composition of that vein will answer a lot of questions (or pose more questions leading to other answers).

Gads, this is like the "who shot JR" conumdrum-- it could go in a half-dozen directions. Matt, talk to your Suits and see if you can toss us a few crumbs as the APXS and MB progress...

--Bill