Could it be a achondrite?

[okstone]

This is a stone found in the desert of Xinjiang, China, with a total mass of 1.5kg, medium magnetism and a density of 2.7g/cm3. One of the pieces is shown in the picture. It looks unusual, and there seems to be a lot of metal highlights < 1mm on the section. The last two pictures were taken under a 500 fold reflected light microscope.

Could it be a achondrite?I will be very grateful.

 

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[DDancer]

There's no evidence of a fusion crust or ablation so I'd be hesitant on it being a meteorite. There's a lot of crystalization evident as well, not a common thing with space rocks. You may want to look at what ASU has to say on your find : https://meteorites.asu.edu/meteorites/meteorite-types/stony-meteorites/achondrites

 

[Red-Coat]

Thanks again for the great pictures. That’s so helpful.

Achondrite meteorites are the most difficult to differentiate from terrestrial rocks because they formed on bodies where essentially the same geological processes that operate on Earth occurred. That means their mineralogy, texture and density are often similar to those of terrestrial rocks. As @DDancer suggests, for an ‘amateur’ without access to specialist testing facilities, an intact fusion crust or other signs of atmospheric flight are the best criteria for identifying possible candidates worthy of further testing. I don’t see that degree of promise here.

Achondrites (stony ones), may have visibly metallic components but, when present, are most usually in the form of small veins rather than specks and spots. These are mostly what we call “primitive achondrites” which covers a number of very rare types. They can have broadly the same bulk composition as chondrites but with an achondritic texture. The type of metallic inclusions you’re showing aren’t at all typical of those classes.

Metallic inclusions of the type you’re showing are something you might see in an aubrite meteorite (sometimes called an enstatite achondrite) and those usually have a crystalline texture which may include greenish olivine similar to the appearance of your specimen. Metal in aubrites can occur as sub-micron sized blebs dispersed in the matrix; as small inclusions within enstatite (up to a few microns in size); as irregularly shaped grains up to hundreds of microns in size; and occasionally as nodules between about 0.2 to 1.5 cm in size. However, aubrites are pretty much invariably brecciated. Usually severely so, attesting to a violent history for their parent body. I don’t see any brecciation in your specimen.

Additionally, the odds of you happening across one of these rare classes of meteorite are low in the extreme. The only way you will be certain is from expert testing, but I would say that this specimen doesn’t have enough positive pointers to warrant that degree of attention.

 

[okstone]

There's no evidence of a fusion crust or ablation so I'd be hesitant on it being a meteorite. There's a lot of crystalization evident as well, not a common thing with space rocks. You may want to look at what ASU has to say on your find : https://meteorites.asu.edu/meteorites/meteorite-types/stony-meteorites/achondrites

Thank you, DDancer. The link you sent is very useful to me.

 

[okstone]

Thanks again for the great pictures. That’s so helpful.

Achondrite meteorites are the most difficult to differentiate from terrestrial rocks because they formed on bodies where essentially the same geological processes that operate on Earth occurred. That means their mineralogy, texture and density are often similar to those of terrestrial rocks. As @DDancer suggests, for an ‘amateur’ without access to specialist testing facilities, an intact fusion crust or other signs of atmospheric flight are the best criteria for identifying possible candidates worthy of further testing. I don’t see that degree of promise here.

Achondrites (stony ones), may have visibly metallic components but, when present, are most usually in the form of small veins rather than specks and spots. These are mostly what we call “primitive achondrites” which covers a number of very rare types. They can have broadly the same bulk composition as chondrites but with an achondritic texture. The type of metallic inclusions you’re showing aren’t at all typical of those classes.

Metallic inclusions of the type you’re showing are something you might see in an aubrite meteorite (sometimes called an enstatite achondrite) and those usually have a crystalline texture which may include greenish olivine similar to the appearance of your specimen. Metal in aubrites can occur as sub-micron sized blebs dispersed in the matrix; as small inclusions within enstatite (up to a few microns in size); as irregularly shaped grains up to hundreds of microns in size; and occasionally as nodules between about 0.2 to 1.5 cm in size. However, aubrites are pretty much invariably brecciated. Usually severely so, attesting to a violent history for their parent body. I don’t see any brecciation in your specimen.

Additionally, the odds of you happening across one of these rare classes of meteorite are low in the extreme. The only way you will be certain is from expert testing, but I would say that this specimen doesn’t have enough positive pointers to warrant that degree of attention.

Thank you, Red-Coat. You're really knowledgeable. I have another larger picture of stone section here. If those silver white highlights in the picture on the first floor are proved to be kamatite or taenite, does that mean it's at least a meteorite?

 

[Red-Coat]

Hi @okstone.

In general, by bulk composition, earth rocks are either very low or very high in total nickel content with nothing in the mid-range. That mid-range is an indicator for meteorites, but meteorites can of course also have very low or very high nickel contents. For isolated native metal (as opposed to general bulk composition) meteorites are also characterised by nickel-iron alloys in one of five forms (two minerals, two subclasses and a mixture). The percentages below relate to nickel content of the metal itself, the remainder being iron with minor percentages or traces of other metals.

Kamacite: (5-10% nickel)

Taenite: 20-65% nickel, but usually 25-40%. At concentrations above 52% it’s usually in the form of tetrataenite, with a specific crystal form arising from slow cooling. At lower concentrations, between 20-40% nickel it may be in a cubical crystal form known as antitaenite.

Plessite: a fine-grained mixture of kamacite and taenite, usually found filling any spaces between them in iron meteorites when both alloys are present.

Inclusions of any of the above are extremely strong indicators for meteorites, but not with 100% certainty.

Taenite also occurs naturally in terrestrial serpentine bodies (the type locality is in New Zealand, but it also occurs elsewhere) and tetrataenite has been reported in terrestrial magnetite bodies from the Indo-Myanmar ranges of northeast India. Nothing reported from China as far as I know.

Kamacite has only two terrestrial occurrences as far as I know: both in China. It’s reported from the Yanshan placer deposits (Chengde, Hebei) where it almost certainly has a disintegrated meteorite origin from an ancient unrecorded impact. It’s also reported from The Chinese Continental Scientific Drilling (CCSD) project (the Main Hole, Maobei, Donghai Co., Lianyungang, Jiangsu) but from rocks that are very deep underground. I think it would be safe to say that, in surface exposures, kamacite is only of meteoritic origin.

For that last rock you’re showing (great picture again by the way) there appears to be a lot of olivine plus various clasts of other minerals. It’s very characteristic of volcanic material… particularly volcanic ejecta and that would be my identification based on what I see. A diogenite meteorite could have that kind of appearance too, but diogenites generally have very little nickel-iron and most commonly are not magnetic. Incidentally, if any of those clasts are quartz then it’s definitely not a meteorite. Quartz crystals don’t occur in meteorites except very rarely, very sparsely, and at sizes you couldn’t see without a high power microscope and expert diagnostics. If you are still keen to pursue the (unlikely) possibility of a meteorite, only expert testing is going to give you a final and definitive answer.

 

[okstone]

Hi @okstone.

In general, by bulk composition, earth rocks are either very low or very high in total nickel content with nothing in the mid-range. That mid-range is an indicator for meteorites, but meteorites can of course also have very low or very high nickel contents. For isolated native metal (as opposed to general bulk composition) meteorites are also characterised by nickel-iron alloys in one of five forms (two minerals, two subclasses and a mixture). The percentages below relate to nickel content of the metal itself, the remainder being iron with minor percentages or traces of other metals.

Kamacite: (5-10% nickel)

Taenite: 20-65% nickel, but usually 25-40%. At concentrations above 52% it’s usually in the form of tetrataenite, with a specific crystal form arising from slow cooling. At lower concentrations, between 20-40% nickel it may be in a cubical crystal form known as antitaenite.

Plessite: a fine-grained mixture of kamacite and taenite, usually found filling any spaces between them in iron meteorites when both alloys are present.

Inclusions of any of the above are extremely strong indicators for meteorites, but not with 100% certainty.

Taenite also occurs naturally in terrestrial serpentine bodies (the type locality is in New Zealand, but it also occurs elsewhere) and tetrataenite has been reported in terrestrial magnetite bodies from the Indo-Myanmar ranges of northeast India. Nothing reported from China as far as I know.

Kamacite has only two terrestrial occurrences as far as I know: both in China. It’s reported from the Yanshan placer deposits (Chengde, Hebei) where it almost certainly has a disintegrated meteorite origin from an ancient unrecorded impact. It’s also reported from The Chinese Continental Scientific Drilling (CCSD) project (the Main Hole, Maobei, Donghai Co., Lianyungang, Jiangsu) but from rocks that are very deep underground. I think it would be safe to say that, in surface exposures, kamacite is only of meteoritic origin.

For that last rock you’re showing (great picture again by the way) there appears to be a lot of olivine plus various clasts of other minerals. It’s very characteristic of volcanic material… particularly volcanic ejecta and that would be my identification based on what I see. A diogenite meteorite could have that kind of appearance too, but diogenites generally have very little nickel-iron and most commonly are not magnetic. Incidentally, if any of those clasts are quartz then it’s definitely not a meteorite. Quartz crystals don’t occur in meteorites except very rarely, very sparsely, and at sizes you couldn’t see without a high power microscope and expert diagnostics. If you are still keen to pursue the (unlikely) possibility of a meteorite, only expert testing is going to give you a final and definitive answer.

Once again, thank you for your wonderful reply, Red-Coat. I tried to use Google translation to understand your answer. I learned a lot about meteorites from you. I think I will fall in love with these rocks from space (although the rocks I have so far are not necessarily meteorites). Thank you.

 

[Red-Coat]

Once again, thank you for your wonderful reply, Red-Coat. I tried to use Google translation to understand your answer. I learned a lot about meteorites from you. I think I will fall in love with these rocks from space (although the rocks I have so far are not necessarily meteorites). Thank you.

You're most welcome. I fell in love with space rocks during the American Apollo missions to the moon. After Apollo 17 it became clear that in my lifetime there would probably never be an opportunity for ordinary people to journey into space. That's when I discovered that even if I couldn't get into outer space, then outer space could come to me and I acquired my first meteorite specimen... more than 40 years ago.

Google translate doesn't always do a perfect job. If you have further questions, please feel free to ask.

 

[okstone]

You're most welcome. I fell in love with space rocks during the American Apollo missions to the moon. After Apollo 17 it became clear that in my lifetime there would probably never be an opportunity for ordinary people to journey into space. That's when I discovered that even if I couldn't get into outer space, then outer space could come to me and I acquired my first meteorite specimen... more than 40 years ago.

Google translate doesn't always do a perfect job. If you have further questions, please feel free to ask.

I went to the local geological organization for analysis, and the results are as follows (the original text is Chinese, I translated it into English with translation software, the translation may not be very accurate):

Mineral composition
Debris 70% ，granularity 2-6mm
Sand debris 17% ，granularity 0.2-2mm
Fillings 13%
Metallic minerals ，a few，granularity 0.02-0.15mm

Feature description
The rock is mainly composed of gravel chips and a small amount of sand chips and fillings.

The gravels are sub prismatic and sub circular. The gravels consist of dacite, granite porphyry and diorite, most of which have been altered. The dacite has porphyry structure, the matrix has spherulite structure, the granite has porphyry structure, the matrix has semi automorphic grain structure, and the diorite has semi automorphic grain structure. The sand debris is also sub angular and sub circular, including quartz debris, feldspar debris and rock debris. The composition of rock debris is the same as gravel debris, with strong alteration.

The fillings are composed of argillaceous material, which has been altered into felsic, chlorite and sericite aggregate distributed among clastic particles.

There are few metal minerals, which are limonite and heteromorphic granular. The results of EPMA are as follows:
FeO:84.47%,TiO2:13.14%,SiO2:1.23%,CaO:0.40%,Al2O3:0.77%。

Structure, mineralization and alteration characteristics: sedimentary rocks

Appraisal Name: altered conglomerate

For this result, the possibility that this rock is a meteorite should be almost nonexistent. My question is, how do so many different kinds of volcanic rock fragments come together to form this rock? It seems to be easier to understand if it is caused by strong impact melting of different rocks.

 

[okstone]

You're most welcome. I fell in love with space rocks during the American Apollo missions to the moon. After Apollo 17 it became clear that in my lifetime there would probably never be an opportunity for ordinary people to journey into space. That's when I discovered that even if I couldn't get into outer space, then outer space could come to me and I acquired my first meteorite specimen... more than 40 years ago.

Google translate doesn't always do a perfect job. If you have further questions, please feel free to ask.

Hi @Red-Coat.

I have some doubts about some parts of the test results, especially that the metal mineral detected by EPMA is limonite. I guess the number of samples at the test point is not enough. I bought a second-hand lithofacies microscope. Through observing the thin rock slices (0.03mm thick) made by the geological organization, the metal minerals mentioned in the electron probe detection results are mainly limonite. I think it is only a part of it, which may be the result of the weathering of part of the metal iron, but some are not weathered.

The following three pictures are the views observed under the lithofacies microscope, which are reflected light, single polarized light and orthogonal polarized light.

Please forgive my English expression ability, I only know some words and grammar, but only with the help of translation software.

These pictures are taken by mobile phone on the lithofacies microscope, which is not clear enough. I think I need a professional photographic equipment and more mineral knowledge.



Reflected light, visual field width is 1.5mm


Single polarized light with a field of view width of 1.5mm


Orthogonal polarized light, with a field of view width of 1.5mm

 

[Red-Coat]

Hi @okstone

I didn’t notice that you had re-posted with more information, otherwise I would have replied earlier. There is a danger of us now getting into a discussion which is way outside the scope of a forum like this, so I will try to keep my answers as simple as possible.

Also (forgive me if this sounds like criticism), but my impression is that you have ‘jumped into the deep end’ by trying to understand your rock from detailed analysis of its composition without an understanding of the more fundamental aspects of geology. Nevertheless, your understanding that this could NOT be a meteorite is 100% correct.

A few basics which might help you understand what type of rock you have. Firstly you need to understand what is know as the ‘rock cycle’, which is shown in diagrammatic form below.



Essentially this shows that all rocks begin with magma (1), which is molten rock. That’s what the Earth was to begin with, and below the surface it still exists and is continually being created.

If that magma cools, it crystallizes and solidifies (2) and then produces igneous rocks (3). There are two types of igneous rocks. Those which form from solidification of magma below the ground which we call ‘intrusive’ or ‘plutonic’… and those which form from solidification of magma on the surface. The magma reaches the surface from rifts in the Earth’s surface or more violently via vents that we call volcanoes. These kinds of igneous rocks we call ‘extrusive’ or ‘volcanic’.

Igneous rock that have formed underground nevertheless can still be seen on the surface of Earth. They get there as a result of plate tectonics, uplifting, and other types of geological movement, or because they have become exposed by erosion. Although igneous rocks are generally hard and resistant, they do ultimately erode and weather (4), producing debris as smaller fragments. If that debris is carried by water, the fragments become progressively smaller and more rounded. Ultimately they will become mud, clay and silt by further erosion and aqueous alteration.

They then accumulate as ‘sediments’ (5) which ae usually water-carried (rain or rivers) and when they become deposited in layers they can become consolidated into sedimentary rocks (6). That happens as a result of drying out, crystallisation of other minerals from groundwater, or as a result of pressure from what gets deposited on top of them.

The cycle continues if those sedimentary rocks become buried and there is enough pressure to create sufficient heat for metamorphism (7), leading to metamorphic rocks (8). If they completely melt (9), they turn back into magma and the cycle starts again.

What the analysis for your rock says is that it’s a sedimentary rock. There are no known sedimentary meteorites. They’re also saying it’s a conglomerate, which is a sedimentary rock composed of small grains of debris from other rocks that have become cemented together. In this case the grains are largely gravel and sand, including at least some volcanic/igneous material, but the rock itself is still sedimentary. You’re effectively at stage (6) in the rock cycle above. The cementing material is said to be argillaceous, which essentially means that it is composed of mud or clay formed by aqueous alteration of other minerals derived from rock fragments.

In short your rock is typical for a mixture of eroded rock fragments which have been water-carried from elsewhere and deposited together with mud as a mixed sediment in an environment where the groundwater was rich in iron… and then solidified as a conglomerate.

I hope that helps a bit.

 

[okstone]

Hi @okstone

I didn’t notice that you had re-posted with more information, otherwise I would have replied earlier. There is a danger of us now getting into a discussion which is way outside the scope of a forum like this, so I will try to keep my answers as simple as possible.

Also (forgive me if this sounds like criticism), but my impression is that you have ‘jumped into the deep end’ by trying to understand your rock from detailed analysis of its composition without an understanding of the more fundamental aspects of geology. Nevertheless, your understanding that this could NOT be a meteorite is 100% correct.

A few basics which might help you understand what type of rock you have. Firstly you need to understand what is know as the ‘rock cycle’, which is shown in diagrammatic form below.

View attachment 1834824

Essentially this shows that all rocks begin with magma (1), which is molten rock. That’s what the Earth was to begin with, and below the surface it still exists and is continually being created.

If that magma cools, it crystallizes and solidifies (2) and then produces igneous rocks (3). There are two types of igneous rocks. Those which form from solidification of magma below the ground which we call ‘intrusive’ or ‘plutonic’… and those which form from solidification of magma on the surface. The magma reaches the surface from rifts in the Earth’s surface or more violently via vents that we call volcanoes. These kinds of igneous rocks we call ‘extrusive’ or ‘volcanic’.

Igneous rock that have formed underground nevertheless can still be seen on the surface of Earth. They get there as a result of plate tectonics, uplifting, and other types of geological movement, or because they have become exposed by erosion. Although igneous rocks are generally hard and resistant, they do ultimately erode and weather (4), producing debris as smaller fragments. If that debris is carried by water, the fragments become progressively smaller and more rounded. Ultimately they will become mud, clay and silt by further erosion and aqueous alteration.

They then accumulate as ‘sediments’ (5) which ae usually water-carried (rain or rivers) and when they become deposited in layers they can become consolidated into sedimentary rocks (6). That happens as a result of drying out, crystallisation of other minerals from groundwater, or as a result of pressure from what gets deposited on top of them.

The cycle continues if those sedimentary rocks become buried and there is enough pressure to create sufficient heat for metamorphism (7), leading to metamorphic rocks (8). If they completely melt (9), they turn back into magma and the cycle starts again.

What the analysis for your rock says is that it’s a sedimentary rock. There are no known sedimentary meteorites. They’re also saying it’s a conglomerate, which is a sedimentary rock composed of small grains of debris from other rocks that have become cemented together. In this case the grains are largely gravel and sand, including at least some volcanic/igneous material, but the rock itself is still sedimentary. You’re effectively at stage (6) in the rock cycle above. The cementing material is said to be argillaceous, which essentially means that it is composed of mud or clay formed by aqueous alteration of other minerals derived from rock fragments.

In short your rock is typical for a mixture of eroded rock fragments which have been water-carried from elsewhere and deposited together with mud as a mixed sediment in an environment where the groundwater was rich in iron… and then solidified as a conglomerate.

I hope that helps a bit.

Thank you again for your wonderful reply. You are very patient in every reply. For beginners like me, I often like to imagine some parts of the earth's rocks as meteorites and jumped into the deep end. I should calm down and study the basic knowledge related to geology.