Matijevic Hill first survey, Sol 3057 - 3152 Options

[Stu]

Oooooh, you're pretty...



Might be here a while, you think?

Edit: better colours on this amended version, I think... http://twitpic.com/apn9s1/full

[Stu]

Oh boy...

[centsworth_II]

Interesting how well those tilted back layers match the red lines in this diagram from a paper by James Wray (interview linked in post 101) et al.

"...phyllosilicate-bearing layers (red lines) exposed in Endeavour rim."

From the text:
"...layers within the western rim dip away from the crater interior, as expected if the beds predate Endeavour crater and were back-tilted by the impact."

"...The Alpha Particle X-Ray Spectrometer could determine major and minor element chemistry, and the Pancam and Microscopic Imager could document grain sizes, shapes, and possible sedimentary textures (e.g., cross-bedding or laminations too fine to resolve from orbit)..."

[xflare]

Looks like things are about to get interesting.

[fredk]

Might be here a while, you think?

Clearly we're at the right spot - the cairn in the middle of your mosaic tells us that!

[mhoward]

Might be here a while, you think?

Wow. Yes, I think so. Unless there's a larger outcrop just down the way or something.

Attached thumbnail(s)

 

[Stu]

Could this be Oppy's very own "Promised Land"..?

[CosmicRocker]

Interesting how well those tilted back layers match the red lines in this diagram from a paper by James Wray (interview linked in post 101) et al. ...

Ahh, so there they are. Beautiful.

... I don't think it was intentional. This happens because the RF steer actuator is locked and when we do a turn in place clockwise the RF wheel plows the soil with the outside wall. When we turn counterclockwise the RF wheel scoops soil in the wheel well. ...

When I first saw the image I assumed it was an intentional scuff, to see what was below the surface.

...sorry about three posts in a row... Mod: merged.

Oh boy...

No kidding. This is perfect timing for a 3D view of this outcrop.

[Stu]

Discuss.

[Stu]

Where did the UMSF Swear Jar go... think we're gonna need it...

[Astro0]

Typical Opportunity. Some other rover gets the limelight for just a moment and she just has to show off.


Good on'ya girl!

[Tesheiner]

I think we'll have a closer look at those rock outcrops.

[ElkGroveDan]

Where did the UMSF Swear Jar go... think we're gonna need it...

It almost looks intentionally placed there to help the story line like a bad sci-fi movie set.

Attached thumbnail(s)

 

[CosmicRocker]

I'm really curious about these mound-like features from the sol 3059 pancams.

-- pano in false color:

-- pancam anaglyph pano:

[NickF]

Sol 3061 navcam pano

[Stu]

Everyone off the bus. I think we could be here a while.

[Tesheiner]

Nice site. Here's the 5x1 navcam mosaic and the respective polar view.

[marsophile]

Very nice images. Are these rubble piles likely to be impact-related?

[Explorer1]

I still see those overhangs as being astonishingly unstable, even in the lower gravity. Watch yourself Oppy!

[RoverDriver]

I still see those overhangs as being astonishingly unstable, even in the lower gravity. Watch yourself Oppy!

One nice thing about 6-wheel driving is that even if one gives way the others pick up the slack. Now if you are talking about IDD, that is a completely different thing. We definitely cannot have one of the wheels on unstable ground while IDD'ing or place the IDD on an unstable rock.

Paolo

[Explorer1]

Yes, the sections on the left (South?) look a lot less foreboding.

[CosmicRocker]

Everyone off the bus. I think we could be here a while.

That, is one strange looking outcrop.

[djellison]

I still see those overhangs as being astonishingly unstable, even in the lower gravity. Watch yourself Oppy!

This outcrop looks about the same size/height as the great wall of Eagle Crater some 8.5 years ago. Nothing the team can't handle.

[dvandorn]

I showed the latest image of this outcrop to my roommate, who pointed out its resemblance to a large pile of, er, thoat droppings.

My hope is that this is the edge of an upturned flap of rock strata that was violently flipped during the impact that formed Endeavour. It looks like the edge of a strata that dips in towards the center of Endeavour, though that's hard to tell with any certainty from this angle.

Anyone think this resembles the Woolly Patch that Spirit studied, which is suspected to have been a small clay outcrop?

-the other Doug

[stevesliva]

Wow - someone wasn't around for Sol 1. This outcrop looks about the same size/height as the great wall of Eagle Crater some 8.5 years ago. Nothing the team can't handle.

Back in the day, young Opportunity was expected to walk to school through thigh-deep snow drifts, uphill both ways.

[Explorer1]

Sorry, I should have been more clear in my post; I was wondering how stable the overhang is if Oppy uses the IDD as Paolo said (we don't know how well attached it is to the surface or what the wind has been doing to it).
I'm know it's nothing that can't be dealt with and I certainly do remember Eagle Crater!

[charborob]

Here's a closeup of the outcrop.

[Stu]

I wonder how much the mission geologists are drooling, looking at these rocks..?



Edit: worked on that a bit more and got rid of that greeny colour... much better here: http://roadtoendeavour.files.wordpress.com...titled-1bv2.jpg

[vikingmars]

I wonder how much the mission geologists are drooling, looking at these rocks..?

Thanks Stu, for this very nice image.
Visually speaking only (no geology), they look like dry clays (very dry and much eroded)... I'm drooling too !

[centsworth_II]

If those are hematite blueberries studding the rocks, then they would be the same ol' Meridiani layers, not pre-impact material. IMHO

[dvandorn]

I'm not yet convinced that the blueberries are embedded into the rocks of this outcrop. They could just be scattered on top of these rocks, either as a lag deposit from previously overlying layers of concretion-bearing rocks that have since been eroded away, or lifted there by aeons of impacts that have redistributed such melt-resistant fragments liberally throughout the area.

A good MI campaign ought to shed more light on whether or not these outcrops have embedded concretions, or just have concretions draped over them.

-the other Doug

[Floyd]

I'm a microbiologist--so what do I know--but to my eye, these don't look like blueberries-not round, not shiny, and the ones that have fallen out look more rounded-cubic or random bits than spherical. The sick green-grey (even with Stu playing with colours) doesn't look like the blueberries we have seen before. I'll go with VikingMars and guess dry eroding clay.

Here is a link to a nice image of eroding clay. With no rain and millions of years of wind erosion, I think we could get what we see in front of Opportunity.

[Tesheiner]

Here is today's mosaic in L2 filter.

[nprev]

Floyd, I agree with you re the berries. First thing I thought was "those sure are tiny & funny-looking blueberries..."

Becoming cautiously excited.

[PaulM]

Interesting how well those tilted back layers match the red lines in this diagram from a paper by James Wray (interview linked in post 101) et al.

...phyllosilicate-bearing layers (red lines) exposed in Endeavour rim."

From the text:
...layers within the western rim dip away from the crater interior, as expected if the beds predate Endeavour crater and were back-tilted by the impact."
...The Alpha Particle X-Ray Spectrometer could determine major and minor element chemistry, and the Pancam and Microscopic Imager could document grain sizes, shapes, and possible sedimentary textures (e.g., cross-bedding or laminations too fine to resolve from orbit)..."

This paper suggest that the strata that Oppy is currently investigating predates the formation of Endeavour Crater.

I understand that the majority of the group of craters of which Endeavour is one are thought to date from the late bombardment. I think that Endeavour is a good candidate for a crater formed during the late bombardment because it is so eroded.

It is therefore possible that the strata that Oppy is currently investigating predates the late bombardment. If the clays formed during the deposition of this strata then this clay might also predate the late bombardment and might therefore be more than 4 billion years old. If this was true then this clay might predate the Gale crater clays by several hundreds of millions of years.

However, I understand that the prefered theory for the origin of these clays is that they formed due to weathering in crevaces after the formation of Endeavour crater and so might be contemporaneous with those of Gale crater.

[Don1]

I'm no geologist, but I'm going with a greenstone/green schist/chlorite schist with embedded garnets. The rock looks finely layered, so maybe it is a schist. The little pebbles could be embedded garnets which have eroded out of the rock. Chlorite is a group of phyllosilicate minerals, some of which contain iron and magnesium. Chlorite could be the source of the Fe/Mg rich phyllosilicates seen in the spectra.

Green schist is a metamorphic rock formed from basalt. Some of the oldest rocks on earth are green schist.

Image here

[ngunn]

Well I'm even less of a geologist than you obviously are but I really like your suggestion. I'd love those things to be garnets - my favourite mineral. However, don't you need huge tectonic movements to produce highly metamorphosed rocks like schist? In favour of the idea: at least schists are hard enough to produce upstanding outcrops, whereas I'd be surprised if eroding clay beds would be.

I expect these rocks to be the progenitors of the clays but not the clays themselves. My reason? A little farther on there is a crater formed into Cape York which CRISM shows to be surrounded by clays (weathered ejecta?) although the interior of the crater appears relatively clay-free.

The Gale crater clays likely have a completely different story to tell. It's an old, old world.

[Stu]

A couple more sections added...

[Zeke4ther]

I think you have the colour balance better here Stu. You can really tell that we have something special here.

[PDP8E]

Here is one of those sub mosaic images of the current formation that OPPY is looking at.
The filters used for this shot are the far infrared, far UV, and plain old green... so my hat is off to Stu for pushing them into something that looks more 'real'. I went with crispness

[Bill Harris]

This paper suggest that the strata that Oppy is currently investigating predates the formation of Endeavour Crater.

{SNIP}

Bingo, Paul.

I've been looking at this outcrop line with interest since leaving the Whim Creek stop. Although we've seen distant views of this zone, my initial impression is that brown-toned layered rocks represent a weathered clastic unit unconformably overlying a basaltic impactite that is pre-Endeavour. This unit was, literally, the paleo-surface of a wetter, warmer Mars. We've had glimpses of it in passing below the basal Burns Formation during the last leg of the pre-Cape York part of the traverse.

Here is a enhanced HiRISE image of this part of Cape York. The area of interest is the light-toned (ie, reddish in the RED-filtered HiRISE image) areas near the center of the image (ESP_024015_1775_RED).

http://i142.photobucket.com/albums/r91/wil...maker_bench.jpg

You can match up the route of the traverse using Tesheiner's Route Maps.

Closer PanCams and MIs are going to be interesting.

--Bill

[CosmicRocker]

Bill: I think the clastic unit underlying the basal Burns formation but overlying the Endeavour ejecta is being unofficially called the Deadwood formation after the target of that name from around sol 2770 or so (near Homestake). It's not exactly what you are talking about, but close. It was discussed in a recent paper that I can't put my fingers on at the moment, but I will try to find it for you.

ngunn: I think I would have to agree with you regarding garnet schist. As much as I'd love to see it, I don't think Mars has been tectonically active enough to have generated much in the way of schist or gneiss.

Right now I find myself agreeing with centsworthII. They look like blueberries to me, though they are on the ragged edge of resolution in these images. Whatever they are, they are embedded in the rock and not just loose granules lying on top. They are resistant to erosion and they are at the head of some mini-yardangs on the surface of the rock, as we have frequently seen with the blueberries out on Meridiani Planum.

We should be able to determine if they are hematite concretions in short order. There is an image set coming from sol 3063 with a full set of right filters...
pancam_Milnet_L234567Rall...
If Milnet is an image of a part of this outcrop, as I suspect it will be, a quick IR ratio image should identify any hematite that may be present.

[walfy]

i tried to stitch a group of these frames together for a 3D, made a headache for the eyes instead! Spectacular outcrop here. The overhanging rock near the top has a nice white vein in it. The rock near the bottom also has such a vein. Perhaps it rolled off eons ago.



And a thanks for the great color panos of these rocks already posted! Really nice work.

[walfy]

Thick blueberry froth!

[serpens]

I expect these rocks to be the progenitors of the clays but not the clays themselves. My reason? A little farther on there is a crater formed into Cape York which CRISM shows to be surrounded by clays (weathered ejecta?) although the interior of the crater appears relatively clay-free.

The

I expect you are right about the rocks being a precursor although that impact possibly excavated a clay bearing layer which is exposed as ejecta while the crater bowl has infilled? No matter how I torture the L257 the clasts seem to have the same response as the matrix so it seems unlikely they are the same hematite concretions as found in the sulphate sandstone. It would be outstanding if this turns out to be pre Endeavour impact materiel and MIs should be real interesting. This ageing rover has stolen the limelight yet again.

[charborob]

Sol 3063 navcam panorama:

[Bill Harris]

It was discussed in a recent paper that I can't put my fingers on at the moment, but I will try to find it for you.

It's a paper by Squyers, et al in Science, IIRC. I can't find it or the reference, tho I may stumble upon it at anytime.

--Bill

[Jam Butty]

Interesting stuff...
looks like there are some thin light colored veins running through the outcrop.

L2R2 flicker gif Sol 3062
Levels stretched to bring out the shadows,


For context its the rock in the top center of this image here...
http://marsrovers.jpl.nasa.gov/gallery/all...LOP2407L2M1.JPG

[serpens]

It was discussed in a recent paper that I can't put my fingers on at the moment, but I will try to find it for you.

The paper was 'Ancient Impact and Aqueous Processes at Endeavour Crater, Mars' Science 336, 570. 'Deadwood' appears to be material eroded from the Shoemaker breccia layer while this outcrop is something new. Is it possible that these are a deposit of (silicate?) impact lapilli - a remnant of the pre Endeavour environment which after all impacted into the ejecta blanket of Miyamoto (and sundry other craters)?

[Stu]

Fascinating place...

[lyford]

For some reason I am thinking of Wopmay....

[Tom Tamlyn]

I was looking forward to this month's Mars Exploration Rovers Update from the Planetary Society's Salley Rayl, which has become our main point of contact with the MER teams. I hope it's simply a little later than usual rather than discontinued. Emily?

[elakdawalla]

I was wondering too, and checked this morning. It's just running late. I'm not sure when we'll get it, but we'll get it!

[CosmicRocker]

... Is it possible that these are a deposit of (silicate?) impact lapilli - a remnant of the pre Endeavour environment which after all impacted into the ejecta blanket of Miyamoto (and sundry other craters)?

I certainly couldn't dispute that hypothesis, given what we now know.

[ilbasso]

For some reason I am thinking of Wopmay....

Funny coincidence! As I was doing the dishes last night, "Wopmay" suddenly came into my mind, and I was remembering the wonderful images as we sidled along Burns Cliff. Seems another lifetime ago...

[TheAnt]

When I first did see these images I did indeed think it might be the actual edge for Endeavour crater.
And made of material that were older than the impact that created Endeavour.

And then reading here that this spot might be related to clays also, even better!
Now that some of you say it might be blueberries here after all, I cannot get the ideas of what we got here to match with each other.
Also I have to admit having a very limited knowledge in geology, I still had the notion that the phyllosilicate layers would not come with blueberries.

[fredk]

Well, the first MI's are down:
http://qt.exploratorium.edu/mars/opportuni...2M1.JPG?sol3064
They are pretty spherical, but they seem to be embedded differently from what we've seen with blueberries...?

And I don't recall seeing outcrops quite like these before:
http://qt.exploratorium.edu/mars/opportuni...5M1.JPG?sol3064
I can't wait to see these in colour...

[charborob]

It really looks like we have two different units here: the dark-colored rock at bottom left and on the left, and the light-colored rock on the right and at upper right:

[Stu]

I can't wait to see these in colour...

You don't have to...

[Jam Butty]

Sol 3064 L257 un-adjusted

[TheAnt]

They are pretty spherical, but they seem to be embedded differently from what we've seen with blueberries...?

I tend to agree that it look somewhat different, lets hear what any of our semi-pro's think.

Perhaps it is so charborob, yet look at this navcam image
http://qt.exploratorium.edu/mars/opportuni...M5P1961L0M3.JPG

The lighter material at left, might be the same as we see at center bottom and in the lower right corner. Those two latter ones might just be less wind eroded.

[mhoward]

Amazing stuff. This is the view west and 20º down.

The "melt"-like stuff reminds me of that one small crater Opportunity explored some months before getting to Endeavour. I'm blanking on the name at the moment. But of course it may be completely different. This looks more like it's part of the rock.

Attached thumbnail(s)

 

[centsworth_II]

...The "melt"-like stuff reminds me of that one small crater Opportunity explored some months before getting to Endeavour.

Maybe you're thinking of these: "Oppy has finished her studies of the Chocolate Hills, and has moved off to the left, resuming her circumnavigation of Concepcion Crater."
Farewell, Chocolate Hills…

But remember, that was melt in Meridiani sulfate rock and we're hoping this is something else.

[Stu]

A couple of MI mosaics...





We really need a "shakes head in wonder" icon...

[ngunn]

They are pretty spherical

. . but range widely in size and seem to like splitting in half. Interesting times.

[dvandorn]

I believe we established quite a while ago that hematite concretions like the blueberries are resistant to melting. This looks like breccia with partially broken-up concretions as the clasts within the breccia. The matrix appears quite uniform.

My best guess is that there were concretions in the soil when the Endeavour impact occurred, and what we see here is impact melt that gathered up the unmelted concretions in the debris cloud as it cooled, making it impact melt breccia with concretion clasts.

In other words, it's blueberry muffin rock.

-the other Doug

[john_s]

Those MIs are astonishing- so fabulous to see something so radically new from a nearly 9-year-old rover! I'm betting against blueberries- these rocks, and the pre-exisiting rocks they might have been derived from in the Endeavour impact, are much older than the blueberry-containing formations so it's perhaps unlikely that they would also have contained blueberries. These guys tend to have resistant outer shells, which I don't think I've ever seen in blueberries (though on oDoug's hypothesis, maybe the outer layers were melted and hardened in the impact?).

I'm betting on these being tektite-like spheres of glassy impact melt...

John

[mhoward]

A couple quick color anaglyphs

Attached thumbnail(s)

 

[centsworth_II]

My best guess is that there were concretions in the soil when the Endeavour impact occurred...

If that's the case they were formed long before the sulfate layer blueberries we are used to seeing and under different circumstances.

[nprev]

What the heck...??!?!! (And, Stu, brilliant work; thanks!!!)

I think that they pretty much have to be blueberries, albeit perhaps of a different vintage than we are used to. They didn't get a chance to get very much larger.

Perhaps a significant clue to the history of the Endeavour impact site.

[Stu]

What the hell...??!?!! (And, Stu, brilliant work; thanks!!!)

Thanks, Nick. You liked that..?

You'll love this...

[CosmicRocker]

Beautiful mosaic.

These appear very different from the blubes we're accustomed to seeing. Glassy impact spherules would be my best guess, too, after seeing the MIs.

We're still missing the R5 filters, so I can't do a hematite image yet.

[dburt]

These somewhat resemble devitrification spherulites (a type of spherule) that form during the localized crystallization of water-bearing glass, although the glass involved is usually more silica-rich (e.g., obsidian) than what was likely the case here. Such spherules can be hollow on the inside, owing to steam released during crystallization; large hollows are called lithophysae. (Many years ago I did much field and theoretical work on lithophysae containing gem topaz.) Spherulites can be more resistant to erosion than the rapidly altering remnant glass that surrounds them. Just another possibility to add to those already suggested.

[Explorer1]

Is that a glint of sunlight on one of the nodules near the top center (of Stu's pan), or just an artifact?
What a place!

[akuo]

What? Another type of spherule in Meridiani? This is just too much. Oppy has clearly been out of the limelight too long, they need to hold another press conference and get Steve there to explain it all.

[atomoid]

Is that a glint of sunlight on one of the nodules near the top center (of Stu's pan), or just an artifact?
What a place!

what a place indeed... Oppy steals the show!!

i think your referring to the right side of the top left quadrant of Stu's wonderful MI mosaic
i see those from time to time, i think its just too bright for the sensor at the exposure level so it bleeds out a bit, perhaps..
im curious about the bloob just to the left of that bright glinting one, it has lines running diagonal to lower right. its kinda really strange, i dont see anythingn quite like it, i dont quite know what to make of it...

the cache of blueberries is so startlingly concentrated here, and since im not a geologist and have no reputation to lose I will go far out on my own breaking limb to suggest they didnt form in situ but were collected by erosional processes rolling into collecting cracks with a subsequent Endeavor impact resultant water percolation cooking them up with rinds and modified materials into something like a blueberry mud muffin cake layer filling, whatever it was it sure looks delicious!!
..but i sure do like the sound of the phrase ".. impact melt breccia with concretion clasts.." (thanks 'other Doug')

[Bill Harris]

These somewhat resemble devitrification spherulites (a type of spherule) that form during the localized crystallization of water-bearing glass...

I've been looking at these spherules and wondreing about the "rind" we see on many of them. You're probably close. Get a larger sample of examples with more images, get some idea of the color, maybe hit a flat surface with the snaggle-toothed RAT to get a fresh x-sectional view. And so forth.

I think these MIs are a view of the light-toned flat rocks, we haven't even gotten to the dark, coarse-textured ones yet!

--Bill


CR: you may be right. On second glance, it's not looking like the light-toned flat rock.

[CosmicRocker]

I'm hoping someone can post a context image showing us where these MI's were taken. It seems that the MIs display a denser concentration of spherules than many of the rocks we see in the pancams.

[CosmicRocker]

What? Another type of spherule in Meridiani? This is just too much. ...

There are an endless variety of spherules. Geologists love spherules.

[serpens]

These have a passing resemblance to the Gunflint Lake lapilli deposit originating from the Sudbury impact. (image source Minnesota Geological Survey). If these are lapilli would that not imply that the deposit was laid down at a distance from the impact site which would be a strong indicator that these were part of the pre-Endeavour impact terrain?

http://i1191.photobucket.com/albums/z468/s...pactlapilli.jpg

[elakdawalla]

I was thinking the same thing. As far as I understand it, a crater rim consists of preexisting target rock layers, usually overturned by the impact excavation process. I would think that most glass would be deposited with the impact ejecta, not in the crater rim. So if these are impact spherules, I don't think they could be from the Endeavour-forming impact, unless Endeavour's current "rim" is not actually the original rim but instead an erosional remnant of the ejecta deposited outside the rim, which turned out to be more resistant to erosion than the actual rim.

But this is all pretty arm-wavey geology. I need to go talk to an impact person, ideally someone who's familiar with the rover mission. I don't actually know anyone who answers that description. Hmm.

[Gladstoner]

.

[belleraphon1]

Know not suppossed to clutter but gotta say WOW OPPY.

Not even going to pretend to be a geologist.

This just proves the benefit of having long lasting rovers..... I remind my non-space following friends that Mars is a world and seeing ONE landing site area does not define the planet.

Keep going OPPY team!!!!

Craig

[Julius]

Could anyone recall the composition of Wopmay back in Endurance crater and the chocolate hills at Conception crater!?? I see a resemblance in these rocks here !!

[Bill Harris]

Blueberries concentrated in a linear outcrop (so it appears) made me think of a clastic dike.

Indeed, this fits very well with the observed textures of the bedding, etc, at this outcrop.

A quick reference to clastic dikes:

http://en.wikipedia.org/wiki/Clastic_dike

They can be relatively benign, like from fluidized injection from the weight of overlying strata, or by the sweeping of sediment into open fractures (like dessication cracks or the Anatolia lineations) or catastrophically, related to impact processes:

http://en.wikipedia.org/wiki/Upheaval_Dome

Your image is labeled "bonner clastic dike"-- what location/formatin is that? "Bonner" makes me think "Idaho".

From yesterday's color Pancams, the Blue of these spherules suggests to me more of an impact melt instead of an hematite concretion. FWIW.

--Bill

[Bill Harris]

the composition of Wopmay back in Endurance crater and the chocolate hills at Conception crater!??

Wopmay was, IIRC, Burns Formation with Blueberry concretions. Chocolate Hills was apparently a fracture fill.

--Bill

[centsworth_II]

Could anyone recall the composition of Wopmay back in Endurance crater and the chocolate hills at Conception crater!?? I see a resemblance in these rocks here !!

Wopmay and Chocolate Hills are altered pieces of Meridiani sulfate layers. These layers were laid down over millions of years on top of the older surface that Endeavour crater was formed on. Hopefully the rocks that Opportunity is looking at now are part of that older surface. If so, although they may resemble Wopmay and Chocolate Hills, they would have a totally different composition and history.

[Don1]

If this rock is Noachian aged, maybe it dates from the period of the Late Heavy Bombardment. Impact lapilli might be common in rocks from that period.

That said, I thought that impact lapilli were supposed to come in discrete layers. These look to be scattered evenly though the rock.

Nobody has said anything about the matrix. I think there is an excellent chance that the matrix is the source of the clays, but last night I compared the route map with the map of the clays from CRISM and noticed that the rover is a little north of the area where clays have been detected.

[ngunn]

(1) I thought that impact lapilli were supposed to come in discrete layers.

(2) I think there is an excellent chance that the matrix is the source of the clays, but last night I compared the route map with the map of the clays from CRISM and noticed that the rover is a little north of the area where clays have been detected.

1/ The upstanding 'fin-like' outcrop could in its entirity be considered a discrete layer. I'm not yet sure whether we are looking at a coherent stack of everted rim bedrock or a rubble-pile of ejecta in which the 'fin' is just one largish fragment that happens to be partly on edge at a plausible angle. Either way I'm with the pre-Endeavour impact lapilli idea for now.

2/ This is quite a small outcrop and any patch of clay minerals deriving from it may be too small for CRISM to resolve. There could still be clays to be found here, though undoubtedly there's a bigger patch up ahead. Will that prove to be associated with more exposures of lapilli-packed rocks? With luck we'll soon find out.

[centsworth_II]

...I thought that impact lapilli were supposed to come in discrete layers....

If they are lapilli, they may have been mixed with other material by impact or some other process, the mixture later becoming lithified.

[Stu]

You can almost feel your boots skidding on these beautiful rocks as you clamber and step over them, can't you..?

[Gladstoner]

.

[CosmicRocker]

... I'm not yet sure whether we are looking at a coherent stack of everted rim bedrock or a rubble-pile of ejecta...

Me, too.
It seemed to me that we should be able to make some guesses about the ages of these rocks from their dips and strikes, so I took a look around.

... If these are lapilli ...?

Lapilli are a very specific type of spherule. Should we expect a certain kind of internal structure in them as compared to glassy spherules?

... unless Endeavour's current "rim" is not actually the original rim but instead an erosional remnant of the ejecta deposited outside...

I'm not sure, but since the apparent rim of Endeavour as seen topographically appears to be discontinuous and significantly eroded (and, since we are all making wild guesses here lately), I'll guess we are somewhat outside of the original rim.

[serpens]

Lapilli are a very specific type of spherule. Should we expect a certain kind of internal structure in them as compared to glassy spherules

From the split examples in the MI they look more like a product of accretion than condensation - maybe perhaps.

[ngunn]

Lapilli are a very specific type of spherule. Should we expect a certain kind of internal structure in them as compared to glassy spherules?

As a non-geologist I'm here to learn from those who are, and I'd appreciate some help with definitions. Here: http://www.google.co.uk/url?sa=t&rct=j...KDA&cad=rja I read that lapilli are small round stones produced by volcanic eruptions or meteorite impacts and that they can be formed either by accretion from a vapour cloud or by solidification of drops of melt. Is that how you're using the term, and if so what is the distinction between the latter case and the glassy spherules you refer to?

(I do apologise for descending into semantics but I want to make sure that my posts do not muddy this fascinating discussion through loose use of terminology on my part.)

[xflare]

Does anyone know of a cross section of a tektite? This is the only image I could find online:
http://www.panoramio.com/photo/3894593

The latest MI shot shows the cross section structure a bit better http://qt.exploratorium.edu/mars/opportuni...M5P2935M2M3.JPG

They do bear a superficial similarity to the very last image on this page http://www.meteorite-times.com/Back_Links/...te_of_Month.htm

[Gladstoner]

.

[dburt]

Tektites are glassy bits of impact melt that hardened in the air; their shape need not be spherical, and they are probably irrelevant to the subject of this discussion. Lapilli are gravel-sized fallen melt stones, without reference to specific shape or origin (only size), and the term alone therefore is ambiguous.

As is being discussed, there are many types of spherules and other intrinsically rounded objects, of various origins. Spherules formed by some combination of chemical and physical accretion, such as concretions (formed by pure chemical accretion owing to abrupt changes in chemical properties of groundwater that reduce mineral solubility) and accretionary lapilli (formed by a combination of condensation and physical accretion - possibly involving electrostatic charge - of particles in a turbulent, cooling and mixing gas cloud, and thus not unlike hailstones in concept) are NOT HOLLOW on the inside, unless perhaps internally weathered or altered (as most are on Earth).

The spherules under discussion, or at least many of them, ARE distinctly hollow, and some appear to have objects in their center. This feature (hollow, possibly with junk on the inside) is characteristic of spherules formed by devitrificationof a hot hydrous glass, especially of the variety called lithophysae. As microcrystallites of anhydrous silicate minerals grow radially outwards, in many cases around a central object or megacrystal that served as a nucleus, they release steam that can inflate the spherule as it grows, leading to a hollow inside (except perhaps for the remant central object). The images haven't shown any yet, but some lithophysae even develop an onion-like or layered outer structure (but with open space between the layers), as a rind of crystallites develops, then steam escapes past it, inflating the still soft hot glass, then another rind of crystallites grows, and so on.

Oppy may have been imaging impact glass cementing breccia ever since it arrived at Cape York. Martian impact glasses and melts, compared to those found elsewhere, should be especially hydrous and full of salts, both of which characteristics would favor devitrification (crystallization), so finding spherules formed by devitrification of hot glass or melt shouldn't be surprising. I repeat, this is just one suggestion among many, and need not be correct, but it appears to be the only one so far that accounts for the intrinsically hollow structure with junk inside and an apparent rind on the outside that has just been imaged here. Greater magnification revealing a concentric outer rind of microcrystallites (as mentioned by Bill Harris above), or new images revealing a separated outer onion-skin structure, both would support the hypothesis. I hope this background information helps the discussion.

[ngunn]

I hope this background information helps the discussion.

It certainly helps me make sense of it. Much appreciated.

[serpens]

After years of sulphate sandstone and a winter looking at a chunk of suevite this is ultra cool. There does not seem to be much deformation in the spherules and if they are devitrified glass wouldn't this indicate a lack of compaction? ie. If they were formed pre-Endeavour then they would have been deposited pretty close to the old surface . A thin section of unweathered rock would come in handy about now. I wonder if the APXS will be able to provide an indication of the nature of the matrix? The next Opportunity related LPSC papers should be real interesting.

Edit: Just to put CosmicRocker's look around in context, is this a view of the outcrop from the Sol 2751 position?

http://marsrover.nasa.gov/gallery/all/1/n/...J7P1907R0M1.JPG