[X] My Assistant

[walfy]

Edit: Replaced the image with a crude stitch of all 4 frames, from sol 3064.

[Zeke4ther]

How odd. Watching that flicker gif, I feel this compulsion to do the time warp. Again.

Brian

A jump to the left! Knees in tight...

[ronald]

Anyone else wonders what this "fibrous" part might be?



Edit: Ahh - only cracks with the right light/shadow combination.

[walfy]

The blueberries from sol 3064 make for great "piku-piku" super GIFs. I was unable to embed one in this forum, but they can all be viewed here.

[Jam Butty]

Nice work walfy,
those piku-piku have come out really well.

[marsophile]

I get the impression that at least half of the "spherules" are hemispheres, though with the shadows it is difficult to be sure.

[dburt]

I get the impression that at least half of the "spherules" are hemispheres...

If the hemispheres are broken spherules, they seem (especially in walfy's excellent 3D renderings above) to possess a distinctive radiating fibrous outer rind or shell, although the resolution could be better. This radiating fibrous texture most resembles the spherulitic texture produced by devitrification crystallization (see photo in Antonb's post #218 and the second photo in my post #237 above), but it might also be caused by other rapid radial growth mechanisms. This texture is not, AFAIK, seen in accretionary lapilli produced by impacts or volcanism, inasmuch these grow by random sticking of particles to a nucleus in a condensing turbulent cloud. It also does not resemble any internal structure seen in broken normal blue hematitic blueberries (nor does the central open cavity). The mystery remains.

[ngunn]

Thanks for the input dburt. But the 'fibres' in ronald's post 367 image are not radial but seem to cross the spherule in approximately parallel directions as if in response to external shear stress after the spherule formed. As to how they formed I notice a nice irony(sorry) here. You say the blueberries formed in mid-air and these spherules formed in situ on the ground whereas if I understand things right most folks seem to be tending the opposite way in both cases.

[serpens]

Anyone else wonders what this "fibrous" part might be?
.....
Edit: Ahh - only cracks with the right light/shadow combination.

The question is why the cracks, which to my overactive imagination seem to have been infiltrated resulting in veining?

ngunn may be right in that the cracks were due to (compaction?) stresses. Or it could be dburt's devitrification crystallization. But I would throw another hypothesis into the mix being rapid quenching of hot glass spherules causing the fracturing. That would of course require that the spherules dropped into water. I remember a paper a few years ago identifying this effect in an impact spherule layer - in South Africa I think. There do seem to be clasts included in some spherules which would point towards glass rich lapilli.

This hypothesis would of course require surface water and since the Miyamoto ejecta would have been hundreds of metres thick here the spherule layer would have to postdate that event. Also this would pretty much rule out the Endeavour impact. So a reasonably thin layer of spherules from another impact could have fallen into surface water overlaying the Miyampto ejecta blanket (the large channels to the south that cut the Miyamoto ejecta do make such a real possibility). This would then make the spherule layer part of the Endeavour uplift rim.

[atomoid]

the fact that so may are semispheres tends to suggest radial crystalization is making them vulnerable to temperature shock induced erosion, otherwise we'd see less halving across the diameters and more random breakage, perhaps a common terran geological observation, no?

[marsophile]

A higher resolution view of the fibrous example, (in parallel stereo).

[dburt]

A higher resolution view of the fibrous example, (in parallel stereo).

Many seem to be confusing these so-called "fibers" (cross-cutting fractures, most likely; I agree with serpens on this) with the far more subtle radial growth textures (that is, super-fine fibrous crystals, at the limit of resolution of the best photos, radiating from the center) seen in the erosion-resistant outer shell or rind to which I was referring above. You have to look carefully at the images to see them. Again, refer to the photos in above posts 218 and 237 (lower photo) to see what I am comparing them to.

[Bill Harris]

My initial impression of the "spherules of unknown affinity" was that they were zeolite, particularly by way of the fibrous radial structure seen in some of the split. I'm not a hard-rock type and this was from ig-met pet courses in school many years ago. I'll always remember the appearance of the hand specimens we had in the lab collection. I recalled that zeolites are secondary minerals created by the interaction of groundwater with volcanic rocks. I've since read up on the zeolite family and it is an interesting mineral.

As I said, I'm a soft-rock guy and I'll need to do considerable research on this or just listen to my betters...

--Bill

[serpens]

My initial impression of the "spherules of unknown affinity" was that they were zeolite, --Bill

You mean formed as a devitrification product? The spherulites seem to be restricted to a reasonably thin layer and glass rich lapilli/devitrification don't seem to be mutually exclusive events particularly if the matrix is also glass.

[dburt]

Zeolites are a good suggestion. My colleague Steve Ruff has argued that they should be widespread on Mars. They commonly form, owing to the action of groundwater, in vesicles (gas cavities or bubbles) in cooling basaltic lava, and in this type of occurrence they are beloved of mineral collectors the world over. They require a more alkaline environment to form than the neutral environment of clay minerals or the acid environment of iron sulfates, owing to their high alkali content.

However, most are distinctly white or light-colored, and although some are fibrous or needle-like (acicular), they only loosely fill the cavities in which they are found. They typically do not constitute the resistant shells. I would therefore be somewhat surprised if the apparently micro-fibrous dark rinds of the hollow spherules in question were made up of zeolite minerals, although on Mars I would hesitate to exclude any possibility. This is all off the top of my head, of course. I'm giving a test and leading a field trip tomorrow, and am running more than a little late.