10 replies to this topic

[lee14]

This example has several characteristics which might lead one to suspect it is a meteorite. The rust color is reminiscent of iron types, it's heavy, and it appears to have the remains of a crust, part of which is still visible.

 

 

The closeup really does look like weathered iron, and it passes the deflection of a suspended-magnet-on-a-string-test, an appropriate, and fairly sensitive field test.

 

 

Here the crust is apparent, much of which is no longer present on the specimen.

 

 

So, why is this not an actual meteorite? First, it fails the appearance test. Despite the color and presence of iron, there are vesicles present, small holes, which are not a feature seen in meteorites. It also doesn't pass the location test, it was not found in a known strewn field, but near a stream. That, with the overall layered appearance and flaking crust indicate a concretion.

 

The potential specimen also does not pass the composition test. When the oxidized iron is tested for the presence of nickel, none is found. The stone is in fact a concretion, a water rounded chunk of limestone upon which a mineral-rich layer has been deposited.

 

Lee

Edited by lee14, 12 December 2020 - 11:37 AM.

[lee14]

Many suspect finds are often prematurely declared to be iron meteorites, well because they're heavy, have a density greater than other stones found in the area, and 'look' like what the general public believes a meteorite 'should' look like. Hematite, an iron mineral, and weathered slag, often found in the vicinity of mining or smelting operations, or in the vicinity of railroad right-of-ways, can mimic the appearance of a rusted iron meteorite. These fail the provenance test (found at random where no confirmed specimens have ever been recovered), do not pass the composition test, either by qualitative chemical analysis or XRF examination (X Ray Florescence, which reveals the various metals present in a sample by an entirely non-destructive procedure), and in fact often do contain other metals normally present in slag introduced during the smelting process.

The image below certainly resembles a chunk of rusted iron, possibly from a forge, severely weathered hematite, or a cast-off scrap from railway construction.

 

 

However, this is a genuine meteorite, indeed heavily weathered, collected at Wolf Creek Crater in Australia. It passes the general appearance test, i.e. is very much the same as other confirmed specimens found at the site. Likewise survives the provenance test, as it was collected and sold by a collector/dealer well known to the world of meteorite dealers and collectors. Levels of nickel are also present, confirming the composition test.

Wolf Creek Crater resulted from the impact of an iron mass estimated at 15 meters in size, 120,000 years ago. This is an arid location, and even so, the oxidation and eventual destruction of these specimens has progressed substantially. This is precisely why no unaltered meteoritic material has survived from strikes that occurred during the first few billion years after the formation of the planet.

 

Lee

Edited by lee14, 12 December 2020 - 12:18 PM.

[eyeoftexas]

Thanks for this.  I would also think that this is quite heavy, which would also cause someone to think meteorite.

[lee14]

Although these would appear to belong in the 'rusted metal chunk' category, they are actual meteorites, in this case Canyon Diablos. They also pass the tests described in the Wolf Creek post. They were recovered by a reliable dealer/collector, and share the appearance of other confirmed specimens of this variety. The elongated and scooped out shapes, with distinct edges, are typical of many Canyon Diablos. The analysis tests were deemed unnecessary here, because they were cut and etched to reveal to internal structure defined by the nickel-iron crystals. Canyon Diablo meteorites are found in the vicinity of Barringer Crater in Arizona, which resulted from an impact estimated to have occurred 61,000 years ago. Also an arid region, they show far less degradation than the Wolf Creek specimen. The two whole pieces below are in 'as found' condition.

 

 

 

The most reliable diagnostic test for confirming an iron meteorite is the presence of a Widmanstatten pattern, revealed by the contrast between the two varieties of nickel-iron crystals present. After cutting and polishing, the surface undergoes an application of nitol, a solution of nitric acid in alcohol. The lack of a pattern does not definitely rule out meteoritic origin, high nickel content types such as ataxites, will often display no pattern at all. The existence of a pattern though is a clear indication the specimen is genuine. Many Canyon Diablos experienced severe shock upon separation from the main mass which had the effect of muting, or even entirely eliminating the Widmanstatten pattern, resulting in a grainy-textured surface strewn with bright narrow bands of metal. The curved pattern in the image below is rarely seen, this specimen suffered an extreme shearing force which distorted the pattern, but was insufficient to compress the piece and eliminate the pattern altogether.

 

 

Lee

 

 

[lee14]

What is the most straightforward test to confirm an iron? Cutting a suspect specimen, if it is an actual meteorite, is not a simple task. Because of the nickel content, this material is significantly harder than ordinary iron, and not something with which an ordinary hacksaw will suffice. The simpler option is to grind a small 'window' onto a relatively flat area of the surface, prepare it with a fine grade of abrasive, and apply nitol with a brush to determine if a Widmanstatten pattern is evident. Again, if no pattern results, it does not necessarily rule out meteoritic origin, but if a pattern is revealed, that would be excellent confirmation. The nickel-iron crystals responsible for the pattern vary in size according to the nickel content, so if it is a type with relatively large crystals, a larger window would be necessary to show a pattern. The smallest crystals are found in fine octahedrites, and when etched display a delicate and easily identifiable Widmanstatten. The image below is of a window polished and etched on a Gibeon. With more care the pattern would show improved definition and have better contrast, but this was simply a casual test to confirm the specimen was in fact a Gibeon, recovered in Namibia. 

 

 

Lee

 

 

[Sincos]

Thanks for the intro to meteorites/wrong posts. Could be pinned to top of forum for a quick check against table of meteorites for those seeking expertise.

[csa/montana]

Nice series for those that really wish to learn about meteorites! 

[SkyHound]

Could some one take a look at this,.

 

A friend found this in a snow-covered field.  It is highly magnetic and the dark areas seem to show melted smooth areas.

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[lee14]

Looks very much like slag.

 

Lee

[leonardovaller]

I'd like to share with you this piece. I bought it about 6 months ago from an unknown dealer. I knew it was a risky. As soon as it came, I was 99% sure it was a fake meteorite.

I still can't identify what exactly it is.

 

• It's a rock
• Same color outside/inside
• It's edged
• Strongly attracts magnets

I was told it's some kind of basalt.

 

What do you think?

 

[peterTH]

It looks like it has flowing patterns, which points to basalt or slag. Same color inside as out is also a no-go for meteorites. Missing crust as well, which is always very very thin if fresh. Old meteorites that have been on the desert floor for thousands of years can get a very thick crust that is mostly rust. Sharp edges are normally not meteorites unless that broke apart on impact.