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The oldest rocks
  
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Roger Warin




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PostPosted: Mar 06, 2014 02:38    Post subject: The oldest rocks  

Hello,
Do you authorize me an off-topic, and yet, not so?
These are the oldest rocks in the solar system. These are refractory oxides and silicates Inclusions. They are called CAI's (Calcium Aluminum Inclusions).
They represent the first condensates from the solar nebula.
Their age was determined in the range of 4.567 and 4.568 billion years (absolute dating Pb) and the condensation time of CAI's lasted about 100,000 years.
CAI’s like fleecy clouds. There are several varieties.
Roger.



Allende#3-0001_R.jpg
 Description:
CAI's
Asteroid belt
 Viewed:  19216 Time(s)

Allende#3-0001_R.jpg



Allende#3-0003_R.jpg
 Description:
CAI's
Asteroid belt
Allende CV3 chondrite
 Viewed:  19271 Time(s)

Allende#3-0003_R.jpg



Allende#3-0005_R.jpg
 Description:
CAI's
Asteroid belt
 Viewed:  19243 Time(s)

Allende#3-0005_R.jpg


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Mark Ost




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PostPosted: Mar 06, 2014 07:59    Post subject: Re: The oldest rocks  

Hi Roger
That must be the most studied meteorite in the world. Perhaps Allende has had pieces of it distributed to most countries. I have a small piece myself which I have often used in teaching or outreach to let the audience set a record for themselves of holding the oldest thing in their hands they have ever held. It also tied in nicely with one of my lessons on how big numbers really are, demonstrating how much larger a billion is in comparison to a million. I related years to seconds, something easier to picture. If you go back a million seconds ago it gets you about 1.6 weeks ago. If you go back a billion you go back........................1982. Now multiply all those seconds by 4. whatever the meteorite is and....................change all those seconds to years..............you get the picture! All of a sudden people start to grasp really how deep time is.

If you really want a headache do the same trick with distance and light years where we go to the trillions.
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vic rzonca




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PostPosted: Mar 06, 2014 08:12    Post subject: Re: The oldest rocks  

Mark Ost wrote:
...If you really want a headache do the same trick with distance and light years where we go to the trillions.

Or dollars.

Yikes!!
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alfredo
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PostPosted: Mar 06, 2014 13:17    Post subject: Re: The oldest rocks  

https://www.bbc.com/news/science-environment-26324968
(link normalized by FMF)
- oldest mineral found so far on Earth, a zircon crystal 4.4 billion years old, which is less than 0.2 billion years younger than the Allende CAIs, and yet older crystals will undoubtedly be found on Earth yet, to shrink the gap a bit more.
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Roger Warin




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PostPosted: Mar 06, 2014 14:25    Post subject: Re: The oldest rocks  

thank you for your comments
Roger.
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Mark Ost




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PostPosted: Mar 06, 2014 17:38    Post subject: Re: The oldest rocks  

Hi Alfredo
Was that from the Jack Hill's down under?
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Mark Ost




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PostPosted: Mar 06, 2014 17:39    Post subject: Re: The oldest rocks  

Roger
What is the blue color in the thin section CAI?
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bugrock




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PostPosted: Mar 06, 2014 18:45    Post subject: Re: The oldest rocks  

Are CAI's composed of named mineral species and do those species also occur on earth?
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Roger Warin




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PostPosted: Mar 08, 2014 17:29    Post subject: Re: The oldest rocks  

Hi,
No, they are not thin sections under XPOL light in my last post. I made some macrophots of a Allende slice with bino. I wanted to compare it with a normal thin section picture.
CAI’s (calcium aluminum inclusion) are nebulous aggregates of refractory oxides and silicates.
Oxides: courundum Al2O3, hibonite (Ca, Ce) (Al, Ti, Mg)12, perovskite CaTiO3, some spinels as MgAl2O4...
Silicates: melilite (Ca, Na)2(Mg, Fe, Al) [(Al, Si) SiO7] (complex group), CaAl2Si2O8 anorthite (feldspar), refractory calcium-clinopyroxene (Al and Ti rich)...
In addition, a subsequent aqueous metamorphism may have altered these minerals partly into garnet (grossular, andradite) or ferrous clinopyroxene as hedenbergite...

There are two large isotopic anomalies in CAI's, the presence of an excess of 26Mg and 16O isotopes.
Roger.



NWA3118_005213_R.jpg
 Description:
CAI's
Thin section + XPol light
 Viewed:  18916 Time(s)

NWA3118_005213_R.jpg


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kakov




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PostPosted: Jun 17, 2017 13:12    Post subject: Re: The oldest rocks  

Dear FMFers,
I understand meteorites to be a kind of taboo subject in our forum, but I interpret this trend as mainly for avoiding the tedious discussions of "is this a meteorite?". The bellow is strictly about a mineral identity; hence I hope to be acceptable.
Please if somebody can give me a hand with confirmation in a puzzle I have been wondering about for several weeks: the identity of the dark crystals I am showing in a CAI (Calcium Aluminum – or refractory - Inclusion) from a CV3 chondrite (surely from North West Africa, maybe NWA 2364 but the detailed meteorite identity is not guaranteed). I can see similar dark grains in the second CAI of the Allende chondrite in the beginning of this string.
I am now inclined to think these dark squared structures are crystals of PEROVISKTE, calcium titanate (CaTiO3). The mineral crystalizes in pseudocubic forms, the cross section of which are expected to be squares. The other option would be the mineral spinel, forming octahedrons, cross section of which could also be squares but I imagine more frequently trapezoid like. The luster also speaks for perovskite, adamantine (diamond-like) or sub-metallic; I think I have observed this luster on the grains under stereolupe. (hardness is much greater on spinel, but this property is difficult to test on small grains)
To be able to compare I tried to search internet for reference photos of perovskite and spinel in CAIs of CV3 chondrites. Unfortunately, I could not find any image focusing on these two minerals. Being relatively common ones in CAIs they usually just show up as secondary actors beside the exotic minerals.

Would anybody here please have any “visual argument” favoring that the grains are perovskite? Thank you very much!

Ps1: The second photo is taken with the meteorite slab immersed under water for around 30 seconds. I was thinking that this might maybe dissolve a little bit of the carbon compounds in the matrix, but I was eager to have a photo with improved contrast of the CAI mineral components.

Ps2: I have a discussion string on this slap in an excellent meteorite forum, CSR, with photos of the broader context in the piece : meteorites(.)ning(.)com/forum/topics/minerals-in-refractory-inclusions-of-a-nwa-cv3-chondrite . So far nobody has confirmed the perovskite identity there, that is why I am raising the same question here as well.

PS3: Another question would be any suggestion for what seems to be a bright rectangular crystal on the top left part of the CAI

CV3 slab kindly lent out by Adrian Contreras



CAI in CV3 NWA chondrite.jpg
 Mineral: Perovskite (?) + probably Melilite Group minerals (white)
 Description:
CAI in a carbonaceous chondrite of CV3 type; size: 9x9mm
In a meteorite from from North West Africa (NWA)
 Viewed:  14498 Time(s)

CAI in CV3 NWA chondrite.jpg



CAI.1.jpg
 Mineral: Perovskite (?) + probably Melilite Group minerals (white)
 Description:
Close up of a CAI (Calcium Aluminum – or refractory - Inclusion) in a carbonaceous chondrite of CV3 type
Field of View: 7 x 6 mm
In a meteorite from from North West Africa (NWA)
 Viewed:  14449 Time(s)

CAI.1.jpg


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Roger Warin




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PostPosted: Aug 05, 2017 03:46    Post subject: Re: The oldest rocks  

Hi,
Excuse me, Kakov, but on June 17, I was in Ensisheim, before going to Sainte-Marie the following week. So I was disconnected from the FMForum during this period.
I appreciate your message. I make an important reservation: my bino is not a spectro or a magic probe.
The macrophotos are taken with a NIKON D800E and according to the size of the samples, I use a Leica MZ6 microscope and better when the size is small, a Leica DM750P equipped with a Leica DFC750 camera. It is important to specify it because the illuminator sends a ray of light of which I do not know the spectrum. In coaxial reflection mode, the use of polarizers is also possible. The sensitivity of the camera must also intervene.
There may therefore be an alteration of the usual colors (or better, a differentiation) which is due to the composition of the target mineral. In crosspolarization, cubic minerals appear black, but also the other minerals that would be microcrystalline, since each component vanishes in this case.
All assumptions of presence of high temperature minerals are valid. For high pressure minerals, we can mention akimotoite (trigonal) and perovskite (orthorhombic). However, this phase is very fragile under the electronic beam and the risk of becoming amorphous is very great.
All these answers can only be provided by a lab.
Note: Peroskite refractivity varies from 2.30 to 2.38 (enormous).
In natural light it will be colorless and sometimes tinged with violet, reddish brown, often zoned.
In polarized light, it will always be off. Its birefringence is abnormal Ng - Np = 0.000 to 0.002.
Roger.
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Roger Warin




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PostPosted: Aug 05, 2017 04:06    Post subject: Re: The oldest rocks  

Hi Kakov,
Ps1: The second photo is taken with the meteorite slab immersed under water for around 30 seconds. I was thinking that this might maybe dissolve a little bit of the carbon compounds in the matrix, but I was eager to have a photo with improved contrast of the CAI mineral components.

It is illusory to dissolve the carbon compounds in water (polar solvent). Carbonaceous products are often condensed polyaromatic rings. Researchers (like those in Munich - Philippe Schmitt-Kopplin, Zelimir Gabelica, Régis D. Gougeon et al., « High molecular diversity of extraterrestrial organic matter in Murchison meteorite revealed 40 years after its fall ») who analyze the thousands of possible compounds do so on methanolic extracts.
Roger.
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