Saturday, January 26, 2013

Is This a Meteorite? How to Identify a Genuine Meteorite


An objet trouvĂ© in my personal collection might be an iron meteorite. It is a very heavy, iron nodule of irregular size and shape. It has a rusty patina and many “regmaglypts” (thumbprints) which are tell-tale indicators of a genuine iron meteorite

There are three main types of meteorites. They are as follows:

  • Iron meteorites these are composed of almost completely metallic material
  • Stony-iron meteorites these have nearly equal amounts of metallic & silicate crystals
  • Stony meteorites these are predominately composed of silicate minerals

Each of these three varieties have more classes and dependent upon the materials that they contain. But the one that I have and am interested in is most likely an iron meteorite.

Although “iron meteorite” implicitly suggests exactly that, I had been under a false impression that a magnet would not necessarily stick to a genuine iron meteorite. It turns out that exactly the opposite is true.
 It is in fact a very rare meteorite that a magnet does not to stick to. This is a good first test to determining whether or not you possess a genuine meteorite. –Does a good strong magnet stick to your rock? Not a cheap little refrigerator magnet; these are nearly worthless for determining this feature. Use a strong magnet.
 Well, my iron nodule in fact is very attracted to a magnet. This does not prove that it is a meteorite, but it adds credibility that it might be.

Another feature of determining a potential meteorite’s pedigree in stony meteorites, is the absence of what are called “vessicles.” These are little pin-prick holes all over the surface or in many regions. If the rock has these, it is an Earth rock and the testing is over.

 Formed most likely by volcanic action, vessicles are formed where gases bubbled out of the still semi-liquid rock before it cooled. Think about how those chocolate “Aero” bars look…full of bubbles. Those little air-holes on a suspected stony meteorite are called vessicles. Meteorites do not have vessicles, only terrestrial Earth rocks do.

Meteorites are quite heavy and dense. They are much denser than typical Earth-rocks of the same size generally. This is almost always everyone’s first exclamation when they first hold a genuine meteorite; they notice that is is quite heavy. This is probably due to greater iron content than any typical Earth rock found on the surface and the lack of porosity (internal gases and voids) inside of the rock.

 During the formation of Earth, heavier elements sank and lighter elements rose to the surface. So most of the heavy stuff sank and it is beyond the typical reach of humans. And, since most ‘stony’ meteors burn up entirely in their fall to Earth and/or are more difficult for the amateur to identify. Iron meteorites are the ones that tend to actually survive the fall and easiest to identify, these are predominately the ones found.

 It is believed that mainly iron meteorites are the ones that formed the really large craters on Earth. And certainly, iron meteorite material is predominately what is found there in the crater. There is of course, fallback breccia, -super-heated Earth crust material that was ejected by the impact and re-solidified in the atmosphere, before falling back to the ground.

Such is the case at the second largest astrobleme on Earth, the Sudbury Basin in Ontario, Canada.

Another strong indicator of a genuine meteorite is a fusion crust, a black crusty ‘shell.’ Often, this shell is incomplete, indicating that the meteorite was part of a larger chuck that exploded either on impact with the surface, or in the air. A stony meteorite with a fusion crust is a lot like a charcoal briquette! Meteors are heated to extraordinary temperatures during their fall to Earth.

 The ablative nature of air friction will cause the meteor to burn, shed debris and form a dark, blank fusion crust. At about 7-miles altitude the air pressure become so great that it literally
'squeezes-out' the flame like blowing upon a lit match and it ceases to burn, and the meteor does what is called a ‘dark fall’ to the ground.

 At this altitude around 7-miles up, the air is very cold so the meteor cools rapidly on its fall to the ground. It is not flaming hot and molten like in the movies, but actually fairly cool to the touch! There are incidents of meteors falling and hitting the roof of homes without causing fire or severe damage (fairly small meteorites, no doubt.) A meteorite can fall upon a frozen lake and not break through the ice!
 A meteorite fall that was in the news recently did exactly this; it crashed onto a frozen lake.

Parts of it are being recovered from a western Province of Canada. Fist-sized black chunks of rock were just lying upon the ice.

A Known Meteorite

a known meteorite

Image Source

Let’s visually examine two known iron meteorites. I chose this image above the one below as they show several striking similarities to the one in my collection that I believe might be an Octahedrite, one of the most common types of iron meteorite.

 Notice the orange-rust patina here and on the image below, and the irregular shape of the one below, and compare to the suspected nodule of mine at the bottom of this article. Very similar, yes?

Another Verified Meteorite

known meteorite

Image Source

An Octahedrite meteorite is composed mainly of nickel-iron alloys “taenite” (of high nickel content) and Kamacite (having low nickel content) with fine-grain mixtures of other compounds in between I note the irregular shape of this.
 This meteorite did a lot of turning and rotating as it burned, -leaving many regmaglypts ‘thumbprints.’ This meteorite was recovered from a desert region where it probably took centuries for the rusty orange patina to form. Again, compare to the image of my suspected item, below.

My Suspected Meteorite

These next two images are of my specimen. These are not the best images, they appear a bit ‘blue’ in these images, much darker and slightly out of focus. -I need a better camera!

I shall try to get better images to replace them. But for now, these will do.

a possible iron meteorite?

(image by author)

I honestly examined this iron nodule for any indication of having been ‘worked’ such as layering or having been hammered, smelted, or having any acetylene cutting torch strata. I do not see any evidence that this was from a foundry or is a ’slag’ waste product of the metal working industry.
 I do see what I had thought was cement or some type of whitish rock material either embedded or adhered to this nodule. I foolishly attempted to dig it out with the sharp end of a nail, hoping to reveal some incriminating evidence that this was a man-made slag. Upon seeing that it is not ‘stuck onto’ the rock but seems to be ‘embedded’ into the iron itself, I ceased my destructive examination.

 One should not attempt to analyze their own suspected meteorite. This is best left to a professional who knows what they are doing. A really good physical specimen with an attractive and unusual shape is of greater value if it is not cut, drilled and worked upon by the unskilled.

What I need to do is have a small, discreet section of this meteorite, -if that is what this actually is, cut and polished and have a nitric acid test done to see if it reveals any Widmanstätten patterns.
 These are called also Thomson structures, these cross hatching patterns of the differing metals. This would verify beyond any doubt that this is in fact, a genuine iron meteorite. Earth iron do not have these structures.

Still Unverified Meteorite

Note the white ’stony’ stuff in the center bowl region. I had attempted to scratch this out with a nail, which sort of detracts from the overall appearance of this. I should have left this alone. It seems to be embedded into the iron, not merely ’stuck to’ the surface as I had thought. Those ‘black dots’ do not appear to be vessicles. They are …black dots. But this is solid material.

Meteors tend to not have 'holes' or 'bubbles' in them, -but 'trapped gases in a meteorite' may in fact, actually occur in some rare cases.

a possible iron meteorite?

(image by author)

Having passed all these ‘quick tests,’ if this is a genuine iron meteorite it would still surprise, me for I found this near a river. Generally, close to water a meteorite would have dissolved, eroded or rusted-away long ago unless it is a very recent event that caused it to be there.

This iron nodule is clearly not a recent fall but it is conjecture to assume that it has been around for hundreds maybe thousands of years. One often finds iron meteorites on dried river beds, tundra or in arid, dry places like deserts. It would be unusual to find a meteorite near active rivers or salty oceans as water (and especially marine waters due to the salt) dissolves the iron rather quickly in geological terms.

 Also, again in fairness, this was found near a railway train line where it might not be uncommon to find discarded iron relics and artifacts. I find no evidence that this is a railway spike, hammerhead or chunk of rail or any such ‘man-made’ jetsam item.
 Every time I just about convince myself that this is man-made and not meteoric material and find myself ready to discard this to the recycling, I find some glimmer of hope, some image or description that mine shares with a genuine iron meteorite.

 Examining this closely again, I see what appear to be minor parallel wavy flow-lines on opposite ends that resemble those of meteorite that fell through the atmosphere, dribbling away its molten outer layer. Small pinnacle points of this are slightly black, with rounded bulbous crowns.
 Again, here is another indication of possibly having burned while falling through the atmosphere. Clearly, I need to move this to the next step and have this iron node authenticated.

Largest Meteor Impact in the U.S.

a U-Haul truck
Image Source

I would have thought that the largest meteor impact site in the United States was at Meteor Crater, Arizona. It turns out that the largest crater in the U.S. in in fact in Chesapeake Bay, off the coast of Virginia as depicted here on the side of the U-HAUL truck.

 U-Haul trucks across the States and Canada feature short facts muraled on the sides of the truck pertinent to states and provinces. These are a great source of featured information.

 All these trucks offer a web site to ‘learn more’ but having checked this URL, all I have found is rental information and nothing to do with the featured murals.
 Pity…
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1 comment:

  1. Your material is most likely 'native-iron' impact slag, chemically reduced to metallic iron in multiple secondary impacts from cometary material sloughed off in the debris path of an incoming comet, most likely the debris path for the Younger Dryas impact, 12,900 years ago.

    This material is quite common (so as to have no monetary value), but is unrecognized as impact slag and therefore routinely dismissed by meteorite labs as 'probable industrial slag'.
    The shape gives it away as a natural object, with whitish (oxidized) basaltic slag, possibly glassy in places like fusion crust, and the forged (left) edge (as though hammered over shows its catastrophic impact origin.

    Your iron rock was likely mined from a round (impact-crater) quarry to access the formerly-molten magnetite, with your iron rock discarded in the waste stream due to the high degree of contamination of the metallic iron with other metallic and non-metallic elements. Much of the basaltic slag with metallic-iron blebs removed from impact quarries has found use as 'clean fill' in roads, paths and rail lines in the vicinity of the quarry.

    Carbon-monoxide comet ice may chemically reduce comet-dust oxides to metallic elements in impact shock waves, but carbonate target rock (limestone or marble) may be required as a fluxing agent for the micro-spherules of metallic iron to merge and form large metallic iron masses like your iron rock, imitating the conditions industrial pig-iron furnaces.

    I suspect two round quarries in Southeastern Pennsylvania (both in limestone terrain) of being impact craters:
    1) Ivy Rock Quarry in Conshohocken, PA and
    2) the round quarry between I-83 and Paxton St. in Swatara Township immediately below Harrisburg, PA.

    Check the terrain in your area on a 'geologic map' for limestone and search "Google Terrain" at a 200 meter scale to look for round quarries.

    For images of other impact slag, click on:
    https://plus.google.com/photos/106045608115852817529/albums?banner=pwa

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