MSL at Rocknest, First scoop samples - sols 57-101 Options

[drz1111]

Exactly, Phil -- what I just called alkali feldspar is the pinkish stuff you find in granites. Of course, on Earth these are formed as a result of subduction, with various rock types including plagioclase being altered under high heat and pressure in the presence of water after the crust has been subducted and then re-exposed by tectonic processes. It would be quite revealing if we were to find significant orthoclase-type feldspar or full-on granitic rocks on Mars, as that would tend to indicate a period of subduction and re-exposure sometime in Mars' past.

-the other Doug

More than that, most processes that generate a granite require water in the partial melting recipe. True granite strongly suggests that you had full-on, Earth-style water-mediated plate tectonics for some period of time.

[Tesheiner]

Created a separate thread for this spectacular self portrait. All posts have been moved there.

[paraisosdelsiste...]

ChemCam shots on Sol 85.

[DFortes]

Note that feldspar is also an important component of basalt, so that's probably the most likely source rock, consistent with what the team says. Feldspar has a wide range of compositions (e.g., anorthosite feldspar is much poorer in sodium and richer in calcium than granite feldspar), and Curiosity can probably tell what kind of feldspar we have here- were any more specifics given at the briefing? Or are there any XRD experts out there who can read that diffraction pattern :-) ?

John

Finally! Something I can contribute to.

First of all - congratulations to the CheMin team for producing the first XRD pattern from another planet, and all credit for anything I say about their work is down to their efforts and those of everyone involved with the mission.

I've done a rather dirty integration of the 2D XRD image that was presented by the CheMin team. I say 'dirty' because I had to play around with the sample-detector distance, which I can't find in any documentation. 18mm seems to work (for the stated wavelength and pixel dimensions), but I'd prefer to have the exact value. Also I haven't been able to do any corrections for detector efficiency or any of that guff.

So, here's the 1D diffraction pattern; as is typical for a real-world bit of rock, with lots of stuff in it, it's quite busy. I've identified the major minerals in the specimen - again, rather crudely (no attempt to scale proportions, or to refine cell parameters) and very much by trial and error. With a properly calibrated pattern I could run it through a database and do the job in 3 seconds.

Nevertheless, you can see quite clearly that the majority of the Bragg peaks are accounted for by either olivine, diopside (a clinopyroxene), plagioclase feldspar, or by parts of the instrument that unavoidably sit in the scattering volume (the X-ray windows, for example). You can also see the broad hump-like background resulting from the presence of amorphous 'stuff'.

The interesting thing is the plagioclase. I do not obtain a good match at all with calcic plagioclase (in other words, with anorthite). However, sodic plagioclase fits rather well with the observed peaks. I've used albite, but some other sodium-rich plagioclase feldspar, like oligoclase would do as well. I'm sure the CheMin folk can refine the cell parameters of this phase and determine with some degree of accuracy what the chemistry is.
Then again, they have XRF data as well...

The occurrence of sodic plag is interesting, and fits in rather well with the press release blurb about Hawaii, since the typical igneous rocks in these settings, hawaiites and mugearites do indeed contain very sodium-rich plagioclase.

Hope that helps

Dom

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[Reckless]

Hi Dom

I had heard that the rock Jake was said to be a mugearite and that oligoclase was maybe associated with it.

Roy F

[DFortes]

Hi Roy
I hadn't heard mugearite mentioned previously, but then I've not seen any of the press conferences, or really kept up with much of this at all. Where did you hear this information?

Interesting that mugearite's type locality is Mugeary on the Isle of Skye, not so very far from Earth's Glenelg.

Dom

[elakdawalla]

This seems like a good moment to post a lengthy explanation on the mugearite identification written by Ed Stolper that Grotzinger sent me. I got it too late to use it in my article and haven't had time to write a blog around it. Enjoy:

First of all, although I will have to sort out how to deal with it, I am indeed quite hesitant about providing a name for any rock based only on its chemical composition. Nevertheless, in this particular case, we will have no choice, and the scientific name will convey a great deal and we would do people a disservice not to provide one. The second issue is that there are many conventions for naming and classifying rocks, and therefore there are several approaches one might take to this for Jake-M.

The starting point for most petrologists in classifying a rock under these circumstances would be to calculate the "norm". What this means is to ask what minerals would be present in a fully crystallized rock (i.e., no glass) of the given chemical composition. This is a somewhat arbitrary exercise, but it has been the starting point for thinking about relationships among igneous rocks for over a hundred years and it gives a lot of insight into what the chemical composition might correspond to in terms of a particular rock. The important result of calculating the norm for Jake-M is that it has significant amounts of the mineral nepheline in the calculated norm: This results in it being classified as an "alkaline" igneous rock. It may not be obvious, but not only in terms of classification but more importantly in terms of understanding how an igneous rock might have formed, this is a critical bit of information. Alkaline rocks are widespread on earth but they are by far not the dominant igneous rock type (nor on Mars based on what we know thus far). Moreover, their origin on earth differs in significant ways from the more common igneous rocks. So to most petrologists and geochemists, the fact that Jake-M appears to be an alkaline composition will be a very important point, especially if it is not a "one off" or an analytical artifact.

Regarding a possible name, there is a well-known and classic sequence of alkaline igneous rocks from alkali olivine basalt, to hawaiite, to mugearite, to benmoreite, to trachyte or phonolite. If one followed the naming used in this sequence (and not everyone would do so), Jake-M is a mugearite based on its overall chemical composition and the mineralogy we might expect based on the calculated norm. Although most geologists would probably have to look up what a mugearite is, well-trained petrologists would not, and the name would evoke for them a great deal about the conditions on earth that would be implied by a rock with this name. (For example, I received an email last night from an old friend asking, based on what he had read in the press, "So is it mugearite, benmoreite or phonolite?") This is one reason my own preference is to call it a mugearite, and I have been doing so inside the MSL team. Again, however, I emphasize that there are other names that others might prefer, including basaltic trachyandesite or phonotephrite (which I would have to look up if someone classified Jake-M as such!). And again, there is potentially great risk in applying a name to a rock out of context that we have not examined for its mineralogy and texture; for example, the use of any of these names assumes it formed from an extrusive rock (i.e., an erupted lava), but it could be an intrusive rock (i.e., it crystallized at some depth below the surface; many of the martian meteorites appear to be intrusive rocks), in which case a different set of names would apply; and there are several other possibilities other than a lava for Jake-M.

There is, in my opinion, a final reason for preferring to call it a mugearite. As you know, the site to which the MSL rover is currently heading was given the name Glenelg. This was because Glenelg is a place name in the Yellowknife region of Canada, but, as I am sure you also know, the original Glenelg is in Scotland, just across from Skye. The "type locality" for mugearite (i.e., the place the rock was first "discovered" or at least defined as a distinctive rock type) is Mugeary, which turns out to be on Skye only 10-20 miles west of Glenelg. The fellow who named the rock type (in 1904) was Alfred Harker, the most influential British petrographer/petrologist of the first third (or so) of the 20th century. Given the nearness of Mugeary and Glenelg, I consider it to be a great cosmic coincidence that on its way to Glenelg, the MSL rover found a rock that can legitimately called a mugearite! And for me, this has special significance because I was a student at the University of Edinburgh in the mid-1970s and spent much time in the Glenelg area (including visiting the brochs there many times) and on Skye.

All this being said, I am still a bit nervous about basing so much on a single chemical analysis, so please remember that caveat.


Ed Stolper

[Reckless]

Hi again Dom

I can't remember the source I think it was from a net based science writer. But after seeing Emily's post the info may have came from the same person as the info in Emily's email seems almost the same as I remember except that I remember the coincidence of Mugeary being about 25 miles from Glenelg instead of 10-20 miles.

Roy

[Explorer1]

Telecon visuals are up:
http://www.nasa.gov/mission_pages/msl/telecon/index.html
I see no smoking gun (except for the helpful 'lab sample' part.

[Hungry4info]

Confirmed, no CH₄ detection just yet. But will continue to gather data.

[xflare]

Confirmed, no CH₄ detection just yet. But will continue to gather data.

I think many were expecting the opposite.

[Hungry4info]

If I understand right, the CH₄ abundance detected from orbit is believed to be seasonal, with the peak detection during summer, so I'm not really surprised. Especially with as early as we are in the mission, with regards to data accumulation.

[fredk]

I hope someone asks how the upper limit on methane compares with the previous measurements. Ie, is it consistent or inconsistent (considering seasonal variations etc).

[Tom Tamlyn]

The prepared presentations have just finished.
IMO, that was an extremely clear, fluent, and well-prepared presentation, rich with information and insights for a lay audience.
* * *
Really good Q&A too. Good questions, and sharp, thoughtful answers.
One other thing the panel did well, and it's one of the hardest things to accomplish, was communicate their enthusiasm persuasively but without distracting goofiness or lowering of the signal to noise ratio.*

Off topic:
Finally, it's great to hear that member Mars Loon (Dr. Ken Kremer), who lives in New Jersey, is well following Sandy.
/off topic
_________
* This is not at all an implied comment on any other MSL press conferences or out-reach efforts; the context is the universe of science communication and journalism generally.

[Hungry4info]

I hope someone asks how the upper limit on methane compares with the previous measurements.

5 ppb was mentioned.
Edit: Someone's asking about it.