Mineral previously only found in lunar samples discovered in WA

[gary]

An article appears online in the Sydney Morning Herald today by Ben Grubb
entitled "Rare moon mineral found in Australia" regarding a paper that has appeared
in the journal Geology.

Abstract of paper here -
http://geology.gsapubs.org/content/40/1/83.abstract

Originally Posted by Ben Grubb, Sydney Morning Herald

Australian scientists have discovered a rare mineral previously known only to be found in lunar rock samples and used it to date an Earth rock which formed over a billion years ago.

Named tranquillityite after the Sea of Tranquility, where astronauts landed on the Moon in 1969, researchers discovered the substance in rocks collected from six sites in Western Australia.

Story here -
http://www.smh.com.au/technology/sci...#ixzz1iT4UIxRu

[Poita (Peter)]

So are they bits of moon that came here from lunar impacts or an old mineral that has been there since the moon was smashed into existence?

[jjjnettie (Jeanette)]

I reckon it's come directly from the moon. There would have been some pretty hefty impacts in the distant past.

[jenchris (Jennifer)]

Aliens brought it here to confuse us

[scopemankit (Chris)]

This could mean that Australia is on the moon!

[Rodstar (Rod)]

The author(s) are probably lunatics.....

[Ausrock (Chris)]

Originally Posted by Rodstar

The author(s) are probably lunatics.....

[renormalised (Carl)]

It's not related to lunar materials blasted to Earth via lunar impacts. It's a late stage crystallisation accessory mineral in igneous intrusions. It forms as the last stages of crystallisation in intrusive dykes and sills. Also, during that crystallisation it's also undergoing secondary alteration to other phases in between the crystals of plagioclase and pyroxene. It occurs in close association baddeleyite and zirconolite within quartz/Kspar intergrowths between the plag and pyroxene laths.

[Baddad (Marty)]

Hi Carl,
This interests me. I am not refuting your point. Why does the report say that the samples are from the Moon? I can understand that the samples can be from anywhere. How has it been determined where the samples are from.
I also can understand that the media wants that attention that the story attracts.

Iridium content is often found in meteorites. Also in igneous deposits. I have not found what kind of concentration differences are expected in the two. It kind of gravitates to iron so I assume that iron meteorites contain more iridium than stony type.
Can you ellaborate on these Carl?

Cheers

[AstralTraveller (David)]

Originally Posted by renormalised

It's not related to lunar materials blasted to Earth via lunar impacts. It's a late stage crystallisation accessory mineral in igneous intrusions. It forms as the last stages of crystallisation in intrusive dykes and sills. Also, during that crystallisation it's also undergoing secondary alteration to other phases in between the crystals of plagioclase and pyroxene. It occurs in close association baddeleyite and zirconolite within quartz/Kspar intergrowths between the plag and pyroxene laths.

Did you notice that the work was done in WA at Curtin and UWA? It was funded by an ARC grant so we paid for it, which I think is money well spent, but then I would - I'm spending your taxes too. Identifying the mineral was obviously not easy because it occurs as "laths up to 150 μm in length and 40 μm in width" and so requires very advanced techniques to examine it. Apart from optical and electron microscopy they obtained X-ray diffraction spectra, something which is normally done on several grams of sample. They also obtained the chemical composition and dated these crystals with a Sensitive High Resolution Ion Microprobe (SHRIMP) which in this case analysed the composition of material ablated from spots 8 microns across.

SHRIMPS themselves are an Australian invention, this first of which was built at the ANU's Research School of Earth Sciences in the late 70's. It took two years to design and five to build and then redesign and modify the first one but now they are 'common' (ie there are at least three in Australia). Their importance is such that the journal Precambrian Research in 2010 devoted a special edition to their impact. In the introduction they note that "In 1983 the risk-taking and years of development paid-off with the first SHRIMP-I peer-reviewed publication which was in Nature (Froude et al., 1983). This was a dramatic debut, as it reported terrestrial Hadean (>4000 Ma) zircons discovered in Archaean metasedimentary rocks at Mt. Narryer, Western Australia".

http://en.wikipedia.org/wiki/Sensiti...ion_microprobe
http://www.science.org.au/scientists...iews/c/bc.html

[renormalised (Carl)]

The original samples from where they identified the mineral, in the first place, came from the Moon. Now they've also found it in terrestrial intrusive rocks.

[AstralTraveller (David)]

Originally Posted by Baddad

Hi Carl,
This interests me. I am not refuting your point. Why does the report say that the samples are from the Moon? I can understand that the samples can be from anywhere. How has it been determined where the samples are from.
I also can understand that the media wants that attention that the story attracts.

Iridium content is often found in meteorites. Also in igneous deposits. I have not found what kind of concentration differences are expected in the two. It kind of gravitates to iron so I assume that iron meteorites contain more iridium than stony type.
Can you ellaborate on these Carl?

Cheers

Marty, I don't see where the article says that the samples are from the Moon. The reason we know that they formed on Earth is that they solidified from a melt, in fact they formed in the spaces between previously-formed minerals (presumably with a higher melting point) and so were definitely not fragments of country rock that were incorporated into the magma. They precipitated from the magma containing all the elements found in tranquillityite, which are in themselves nothing special. It is just that at a certain point in the cooling of the magma the conditions (temperature, pressure ...) were right for this particular mineral to form.

[renormalised (Carl)]

SHRIMPS.....damn good bits of kit. Yeah, minerals of that scale can be pretty damn hard to identify because they're so small you can't really tell what they are, and trying to find enough to analyse is a pain. Been there, done that

[Baddad (Marty)]

Thanks David,

My mistake. The penny dropped. Heading was moon rock in WA etc. Media sensationalism.
I assume that all moon rock would be igneous. (Plus impacts by meterorites.) Although the moon is stable it once was a very hot place.
The cooling process would be slow due to the mass.
The side facing Earth may have cooled at a different rate to the "dark side". Would you expect the rocks to be different on the dark side?

Cheers

[AstralTraveller (David)]

Originally Posted by renormalised

SHRIMPS.....damn good bits of kit. Yeah, minerals of that scale can be pretty damn hard to identify because they're so small you can't really tell what they are, and trying to find enough to analyse is a pain. Been there, done that

Did you use a SHRIMP?? We've had a couple of students use the ANU SHRIMP recently. I'll check tomorrow but I think when my boss was at RSES he worked on building a SHRIMP. I remember him saying that they estimated that there were about a million individual pieces in the instrument ... and they all have to be 'just so' or it won't work. No wonder technicians go gray and drink.

[Baddad (Marty)]

That's so right David,
I'm gray (grey) and I drink.
It seems to be a common hazard of the occupation.

[AstralTraveller (David)]

Originally Posted by Baddad

Thanks David,

My mistake. The penny dropped. Heading was moon rock in WA etc. Media sensationalism.
I assume that all moon rock would be igneous. (Plus impacts by meterorites.) Although the moon is stable it once was a very hot place.
The cooling process would be slow due to the mass.
The side facing Earth may have cooled at a different rate to the "dark side". Would you expect the rocks to be different on the dark side?

Cheers

Given that the Moon's mass is unevenly distributed (hence the gravitational locking) the distribution of heavy vs light minerals is obviously not symmetrical but I'd be surprised if there are different minerals in each hemisphere. Of course there is a lot we don't understand about the Moon including why the two hemispheres have dramatically different topography. And so there was a satellite (or pair of satellites), whos name escapes me, launched recently which will map the gravitational anomalies with much greater accuracy than previously in an attempt to understand the Moon's internal structure and thus (amongst other things) why the differences.

[renormalised (Carl)]

No....there was only one around and not at JCU. I was using an xray diffractometer and an EPMA (Electron Probe Microanalyser) to look at the samples I had. Wish we had've had a SHRIMP. I could see what I tentatively identified as zircons in my sample, but they were that small they were hard to identify and very hard to analyse. There were also some very small biotite crystals with fission tracks in them...not much larger than the zircons. Would've been good to have been able to get a date on them.