NEW INFO on my "Meteorite" - I got Iron and I got Nickel

[Steve in PA]

I have posted a couple threads over the last two weeks about the rock that set my metal detector off in a plowed field. I had polished a spot on the rock with my bench grinder and tried to get an elemental analysis with our hand held PMI gun at work, although I am not trained to use it and it is much less accurate that our larger one that actually burns the surface of the material.

Today we had the technician back in the office that is trained to use this equipment and he took a reading using our Oxford PMI Master Pro Mobile Spectrometer.


Here is the spot that was tested before and after the burn


And here are the results: 33.2% Iron, 14.0% Nickel - I think there is still hope for this rock

 

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[Terry Soloman]

Do you have a local college with a Geology department? See if they will look at it.

 

[Steve in PA]

I might check with the Carnegie Museum of Natural History here in Pittsburgh. We also have the University of Pittsburgh, and Carnegie Mellon University here.

 

[Red-Coat]

I can’t say how accurate that analysis might be but – taking the measured amounts at face value – there are multiple indications that your specimen is not a meteorite. Here’s just a few:

Although the specimen is high in total metal, the silicon content is only 1.37% which tells us that it could not be a stony chondritic or achondrite. Also, the highest total metal content among those two groups is found in H-Group chondrites, where it ranges between 15-20% by mass, whereas your specimen is way outside that range. The nickel portion would be between 1.0-1.8% of the total metal content and nowhere as high as your measured 14%

Just because you have now found nickel in association with iron does not mean that you have a meteorite. The reason they are found together is that nickel is highly siderophilic (‘iron-loving’) and the reason that many other metals are conspicuously absent or present in very low amounts is that they are lithophilic (‘stone-loving’). Lithophilic metals therefore form ‘abundances’ in the silicate portions of meteorites, not the metallic portions and we already know your specimen is low in silicon.

Apart from iron and nickel, the other native metallic components of meteorites are generally low: cobalt in amounts up to about 2%, copper in amounts up to about 0.02%, plus traces of manganese and tin. Other metals would be in ppm or ppb, or below the limit of detection. The percentage values found in your specimen: chromium 4.4; niobium 2.22; manganese 2.13; titanium 0.855; molybdenum 0.835; cobalt 0.753; vanadium 0.738; copper 0.654; tungsten 0.533; lead 0.308; and aluminium 0.153 are way above anything that could be found in a metallic meteorite (with the exception of the cobalt content).

Just as one glaring example, a level of 2.22% niobium would be a truly extraordinary thing in a meteorite of any kind. When we talk about ‘abundances’ in elemental terms, that’s a comparative word relative to expected amounts of what are rare elements. Niobium is lithophilic but may be weakly siderophilic under some circumstances of high temperature and pressure but only occurs at ‘abundances’ around 0.5ppm associated with the silica in stony meteorites and only up to about 50ppb in iron meteorites.

It's true that from time to time a meteorite turns up with analytical values outside our expected or known ranges... but not with such a large number of extreme anomalies as evidenced here and which defy everything we think we know about how meteorites of various types were formed.

 

[Steve in PA]

I can’t say how accurate that analysis might be but — taking the measured amounts at face value — there are multiple indications that your specimen is not a meteorite. Here’s just a few:

Although the specimen is high in total metal, the silicon content is only 1.37% which tells us that it could not be a stony chondritic or achondrite. Also, the highest total metal content among those two groups is found in H-Group chondrites, where it ranges between 15-20% by mass, whereas your specimen is way outside that range. The nickel portion would be between 1.0-1.8% of the total metal content and nowhere as high as your measured 14%

Just because you have now found nickel in association with iron does not mean that you have a meteorite. The reason they are found together is that nickel is highly siderophilic (‘iron-loving’) and the reason that many other metals are conspicuously absent or present in very low amounts is that they are lithophilic (‘stone-loving’). Lithophilic metals therefore form ‘abundances’ in the silicate portions of meteorites, not the metallic portions and we already know your specimen is low in silicon.

Apart from iron and nickel, the other native metallic components of meteorites are generally low: cobalt in amounts up to about 2%, copper in amounts up to about 0.02%, plus traces of manganese and tin. Other metals would be in ppm or ppb, or below the limit of detection. The percentage values found in your specimen: chromium 4.4; niobium 2.22%; manganese 2.13; titanium 0.855; molybdenum 0.835; cobalt 0.753; vanadium 0.738; copper 0.654; tungsten 0.533; lead 0.308; and aluminium 0.153 are way above anything that could be found in a metallic meteorite (with the exception of the cobalt content).

Just as one glaring example, a level of 2.22% niobium would be a truly extraordinary thing in a meteorite of any kind. When we talk about ‘abundances’ in elemental terms, that’s a comparative word relative to expected amounts of what are rare elements. Niobium is lithophilic but may be weakly siderophilic under some circumstances of high temperature and pressure but only occurs at ‘abundances’ around 0.5ppm associated with the silica in stony meteorites and only up to about 50ppb in iron meteorites.

It's true that from time to time a meteorite turns up with analytical values outside our expected or known ranges... but not with such a large number of extreme anomalies as evidenced here and which defy everything we think we know about how meteorites of various types were formed.

Thanks for your detailed analysis. I don't know how much stock we can put into some of the lower values. Still one thing troubles me. Iron and Nickel do not occur together in terrestrial rocks....
More than 95% of all meteorites contain iron-nickel (FeNi) metal. “Iron-nickel” means that the metal is mostly iron but it also contains 4-30% nickel. The metal occurs as two different alloys known as kamacite (lower nickel concentration) and taenite (higher nickel concentration). Both alloys strongly attract magnets. Neither alloy occurs naturally in Earth rocks, so a natural rock that contains kamacite or taenite is a meteorite.
https://sites.wustl.edu/meteoritesite/items/metal-iron-nickel/

 

[Red-Coat]

...Still one thing troubles me. Iron and Nickel do not occur together in terrestrial rocks....

That’s untrue. If we’re talking ores where the metals are present as mineral compounds then iron and nickel most certainly do occur together. The unwanted tailings from iron ore mining often contain significant amounts of nickel, particularly for ores high in sulphides. Pentlandite for example is an iron–nickel sulphide that usually has a 50:50 ratio of iron to nickel. As a pure mineral it’s non-magnetic but often occurs with other iron minerals including magnetite. Limonite also often contains 1-2% nickel,

If we’re talking native metals then it’s also untrue, but natural occurrences of terrestrial nickel-iron are rare and have a limited distribution. Since nickel is highly siderophilic, most of Earth’s native nickel has migrated with the iron to form our planet’s core and probably a substantial portion of its mantle, admixed with siliceous rock. That’s also the reason for the composition of nickel-iron meteorites since, in a sense, they represent the cores of failed planets (and pallasites are representative of what would have been the mantle).

The net result is that Earth’s crustal composition has been depleted of these native metals and much of what once existed has also been converted to oxides, sulphides etc. However there are still areas of Earth where both metals exist in native form. Telluric iron is extremely rare, with Greenland as the only major deposit, and contains up to 4% nickel. Silicated iron nodules with various proportions of nickel also occur in other areas of the extreme northern hemisphere, such as Arctic Canada/Alaska and Siberia. In other areas of the world native nickel-iron alloys exist, with nickel contents usually between 24-77% and with different (synonym) names according to location. In the US, the main deposits are in Josephine & Jackson Counties, Oregon where it’s known as ‘Josephinite’ (although the type locality is in New Zealand where it was originally named ‘Awaruite’). The composition typically varies between Ni2Fe and Ni3Fe and in Oregon it’s found in sizes from small nuggets up to large ellipsoidal masses weighing 40 kilograms or more.

Note that I chose my words carefully. I didn’t say that your specimen was terrestrial (ie naturally-occurring). Only that it was not meteoritic. The analyses for the metals it contains cannot possibly be meteoritic (if they’re correctly reported). I leave open the question of whether your find was from an area where native nickel-iron alloys are a possibility. If your specimen is a chunk of something man-made or smelted, then almost any composition is possible and location then plays no real part in identifying it.

 

[Steve in PA]

That’s untrue. If we’re talking ores where the metals are present as mineral compounds then iron and nickel most certainly do occur together. The unwanted tailings from iron ore mining often contain significant amounts of nickel, particularly for ores high in sulphides. Pentlandite for example is an iron–nickel sulphide that usually has a 50:50 ratio of iron to nickel. As a pure mineral it’s non-magnetic but often occurs with other iron minerals including magnetite. Limonite also often contains 1-2% nickel,

If we’re talking native metals then it’s also untrue, but natural occurrences of terrestrial nickel-iron are rare and have a limited distribution. Since nickel is highly siderophilic, most of Earth’s native nickel has migrated with the iron to form our planet’s core and probably a substantial portion of its mantle, admixed with siliceous rock. That’s also the reason for the composition of nickel-iron meteorites since, in a sense, they represent the cores of failed planets (and pallasites are representative of what would have been the mantle).

The net result is that Earth’s crustal composition has been depleted of these native metals and much of what once existed has also been converted to oxides, sulphides etc. However there are still areas of Earth where both metals exist in native form. Telluric iron is extremely rare, with Greenland as the only major deposit, and contains up to 4% nickel. Silicated iron nodules with various proportions of nickel also occur in other areas of the extreme northern hemisphere, such as Arctic Canada/Alaska and Siberia. In other areas of the world native nickel-iron alloys exist, with nickel contents usually between 24-77% and with different (synonym) names according to location. In the US, the main deposits are in Josephine & Jackson Counties, Oregon where it’s known as ‘Josephinite’ (although the type locality is in New Zealand where it was originally named ‘Awaruite’). The composition typically varies between Ni2Fe and Ni3Fe and in Oregon it’s found in sizes from small nuggets up to large ellipsoidal masses weighing 40 kilograms or more.

Note that I chose my words carefully. I didn’t say that your specimen was terrestrial (ie naturally-occurring). Only that it was not meteoritic. The analyses for the metals it contains cannot possibly be meteoritic (if they’re correctly reported). I leave open the question of whether you find was from an area where native nickel-iron alloys are a possibility. If your specimen is a chunk of something man-made or smelted, then almost any composition is possible and location then plays no real part in identifying it.

Well I think I will hold onto this rock, and maybe one day I can find out exactly what it is