Meteorite testing

I do not test or classify meteorites

I do not test rocks to determine if they are meteorites. I do not classify meteorites and I do not provide “Certificates of Authenticity.” I am a retired geochemist and I no longer have a laboratory. Do not send me samples.

If, on the basis of the information that you provide me, I think that your rock might be a meteorite, then I can probably put you in contact with someone who does classify meteorites. I will not do that, however, unless I am >95% certain that the rock is, in fact, a meteorite. It will likely cost you several hundred dollars to have it classified because classification requires a lot of time on expensive laboratory instruments. For amateur finders it is more convenient to find a meteorite dealer who will buy it unclassified as the dealer will have contacts who can classify it. Be aware, however, that most meteorite dealers will ignore you because, like me, they are contacted every day by sincere persons with meteorwrongs.

Alternatively, click here. This is the list from the Meteoritical Bulletin Database of all the meteorite names that have been approved in the past 6 months. If you click on the name of a meteorite, you can find the names and institutions of the persons who classified the meteorite. You can try to contact classifiers directly. You almost certainly will be ignored, however, unless you make a convincing case that your rock is, in fact, a meteorite. Follow my advice below about testing. All classifiers are besieged with requests from well-meaning but overly optimistic persons who have found meteorwrongs. Most classifiers will only accept samples from experienced finders and collectors who have a record of recognizing a meteorite when they see one.

Stony meteorites

If you are particularly certain that your rock is a meteorite and you really want to convince me or any other scientist, then I urge you to obtain a chemical analysis at a commercial rock-testing laboratory. There are many labs around the world that can provide such tests. At a minimum, I need “whole-rock” data for the major rock-forming elements: Na₂O, MgO, Al₂O₃, SiO₂, K₂O, CaO, TiO₂, Cr₂O₃ or Cr, MnO, and Fe₂O₃ as well as trace elements Ni and Co.

Please

Do not bother Actlabs (or any other lab) with questions about meteorite identification. They are chemists who are experts in rock analysis. It is not their job to interpret results. They have no one on staff who is a meteorite expert. They do not classify meteorites. They do not offer “Certificates of Authenticity.” I am the meteorite composition expert, which I do for free. Actlabs sends persons with meteorite questions to me.

A portion of an Actlabs report sent to me by a rock prospector. The first elements I look at are SiO₂, Fe₂O₃(T), Na₂O, K₂O, Cr, and Ni. This rock is not a meteorite. SiO₂ concentrations in stony meteorites are typically 35-57%. Fe₂O₃(T) [total iron expressed as Fe₂O₃] is typically 15-40% except that lunar meteorites can be as low as 3%. Except for some martian meteorites, Na₂O is almost always <1% and K₂O is always <1.5% and typically 0.1% in ordinary chondrites. A characteristic difference between terrestrial rocks and meteorites is that meteorites have high Cr concentrations, typically 1000-8000 ppm, except for a few lunar and martian meteorites, whereas terrestrial rocks typically have <500 ppm. Chondritic meteorites have 10,000-18,000 ppm Ni. This rock is probably a granite or closely related rock like dacite or rhyolite.

Check your own data with Chemical composition of meteorites.

July, 2022: I have received results of analyses of 672 samples from Actlabs and more than 140 samples from other labs. Only 9 of the rocks have been meteorites, 6 ordinary chondrites, 2 iron meteorites, and 1 pallasite. More than half of these rocks were from northern Africa or the Middle East and a couple, I believe, were stones that someone had bought or inherited.

Wavelength dispersive X-ray fluorescence spectrometry (WDXRF)

X-ray fluorescence (XRF) spectrometry (also known as XRF spectroscopy) has been used for decades as a means of determining the elemental composition of rocks. Historically it has been a laboratory technique requiring a large instrument that generates an intense beam of X-rays from an X-ray tube. Samples are typically ~1 gram (0.25-5 g) of pressed rock powder or glass made from melting of rock powder. The entire sample is exposed to the X-ray beam. The primary X-rays excite secondary X-rays in the rock sample. Each element diffracts secondary X-rays of characteristic wavelengths in different directions. The detector is moved in a circular path about the sample counting x-rays emitted by each element individually. This technique is known as wavelength dispersive XRF (WDXRF) spectrometry. When used by experts it is very accurate and precise, on the order of 1-2% for elements occurring at concentrations of 1% or greater as well as several trace elements of lower concentration. Other advantages are that a large fraction of the elements in the periodic table can be determined and, because the sample is powdered, the results will be more representative of the whole rock than those from a technique using spot or beam analysis (below). Wavelength dispersive XRF is mainly done in commercial and university labs as well as by mining companies. Note, however, that WDXRF does not determine concentrations of elements that occur only in parts-per-billion (ppb).

Energy dispersive X-ray fluorescence (EDXRF or EDAX)

EDAX or, more properly, EDXRF – energy dispersive XRF – is a cheaper alternative. Such data are commonly obtained with a scanning electron microscope (SEM) and bench-top instruments. In these instruments a small (usually much less than a millimeter) electron beam is aimed at the sample and all the emitted X-rays are collected with a detector that sorts the X-rays in order of increasing energy to yield an X-ray spectrum. Alternatively, there are instruments that use either small X-ray tubes or radioactive sources that emit gamma-rays as the excitation source. Again, however, the detector “sees” all the emitted X-rays at once and sorts them by energy producing an energy spectrum.

For the purpose of identifying meteorites there are three main problems with EDXRF.

The energy resolution is considerably worse for EDXRF than for WDXRF. For example, because iron (Fe) and nickel (Ni) are adjacent to each other in the periodic table, the spectral peaks overlap in EDXRF and are, consequently, more difficult to quantify. Also, in EDXRF identification of peaks is sometimes ambiguous as minor peaks from major elements overlap and interfere with major peaks from minor and trace elements. In the wavelength spectra obtained by WDXRF, the peaks are much narrower and there are fewer peak overlaps so identification is much less ambiguous.
The excitation sources used in EDXRF are weaker than that from the X-ray tubes used in WDXRF, thus longer count times are required to accumulate the same number of counts. Precision improves as the number of observed counts increases. Elements occurring at abundances of <5% are sometimes not determined with enough statistical precision to be useful or are not observed at all.
In EDXRF, unless the sample has been ground to a fine powder, a spot analysis is obtained, not a bulk (whole-rock) analysis as in WDXRF. We need to know the bulk composition, not the composition of several small spots that may only represent individual mineral grains. If the beam is at least 2 mm in size or the beam is rastered, an ordinary chondrite could likely be distinguished from a terrestrial rock with EDXRF data. It would not be possible, however, to definitively recognize most achondrites as meteorites.

Bottom line: Data obtained by EDXRF are often not sufficiently accurate, precise, or complete to distinguish a meteorite from a terrestrial rock.

Handheld XRF analyzers

Several persons, before contacting me, have brought their rocks to a scrap-yard dealer, mining company, gemologist, coin shop, or jeweler to have them tested with a hand-held “XRF gun” or other handheld XRF analyzer. These instruments are miniature EDXRF analyzers. Because of the issues discussed above, most of the results that I have been sent from such analyzers have not been useful for determining if a rock is a meteorite. Also, there are at least three additional problems with hand-held devices that lead to results that are somewhere between misleading and highly erroneous:

Most of the instruments are designed or programed to do analysis of ores and metals for metallic elements, e.g., Cu (copper) Zn (zinc), and Mo (molybdenum) for miners, Cd (cadmium), Pb (lead), and W (tungsten) for scrap-yard dealers, and Rh (rhodium), Au (gold), and Pt (platinum] for jewelers and coin shops. These modes focus on elements that are useless for stony meteorites because the concentrations of all these elements in meteorites are much lower than the analyzer can actually detect (parts-per-million or parts-per-billion) in rocks. To determine if a rock is a meteorite, we need to know the concentrations of the major rock-forming elements: Si, Al, Fe, Mg, Ca, Ti, Mn, and (ideally) Na, K, and Cr as well as the trace element Ni. In “metals” mode, for example, hand-held XRF analyzers typically do not report data for Si (silicon) or Ca (calcium), critical elements for determining if a rock is a stony meteorite.
Second, data for Na and Mg are also critical to distinguish earth rocks from meteorites and those elements cannot be determined by X-ray fluorescence in air. (I have received data from a gemologist reporting 46% magnesium in a rock. That is just plain wrong.)
Third, some of the common analyzers are not designed to analyze rocks and for those that are many users do not know enough about rocks to set up the device properly or interpret the results. The worst case that I have encountered was a fellow who contacted me saying “Big time reputable gold dealer tested it with his X ray gun.” The gold dealer told him that his rock contained “at least 15% Bohrium,” an element that does not occur as a stable element in nature and the only isotope of which has a half-life of ~85 milliseconds. (I suspect that the instrument actually reported boron, not bohrium.) Sorry, there is no polite way to say this: few scrap yard, jewelry store, or coin shop people know anything about rock analysis.

Left: This is what happens when a silicate rock is examined in “precious metals” mode (top blue line). Silicate rocks are composed mainly (typical total of 90-98%) of the elements O, Si, Ti, Al, Fe, Mg, and Ca. Except for Fe (iron), none of these elements were “seen” by the instrument in the photo because the instrument was not set to look for them. Elements erroneously identified in the display as Pt (platinum), Rh (rhodium), Cd (cadmium), Ni (nickel), and Pb (lead) are probably based on spectral peaks of interferences from the major rock-forming elements. Except for Fe, the elements listed in the display do, in fact, actually occur in the rock but only at parts-per million or parts-per-billion levels, not percent (%) levels as the display erroneously reports. These rare elements cannot be detected by EDXRF in the presence of the major rock-forming elements. “Precious metals” mode should only be used on metal samples, not rocks.

The abundances of platinum-group elements are much higher in meteorites (e.g., part-per-million levels in chondrites) than in terrestrial rocks (part-per-billion levels) but they cannot be detected by XRF in any rock because the concentrations are much below the detection limits of the instruments.

X-ray diffraction (XRD)

People also send me results obtained by X-ray diffraction. XRD identifies the major minerals in a rock, not the chemical composition. In my experience, XRD results are often ambiguous. Some minerals that occur in meteorites largely do not occur at all in terrestrial rocks. So, the identification of, e.g., kamacite or troilite would be strong evidence that a rock is a meteorite. These two minerals are common in iron meteorites. Most of the minerals that are unique to meteorites are nevertheless minor to rare in stony meteorites and may not be detected by XRD. The three most abundant minerals in stony meteorites are olivine, pyroxene, and plagioclase. These three minerals are also among the most common minerals in terrestrial igneous rocks. Some minerals that are common in terrestrial rocks are rare to absent in freshly fallen meteorites, however. Quartz, calcite, micas, and clay minerals are good examples, so the detection by XRD of any of these minerals as major phases in a rock is largely conclusive that the rock is not a meteorite.

Bottom line: XRD can often prove that a rock is not a meteorite but it rarely provides unambiguous evidence that a rock is a meteorite.

Laser Raman spectroscopy

A few people have sent me results obtained by Laser Raman spectroscopy. Like XRD, the technique identifies minerals, it does not determine the composition. LRS certainly has its uses in meteorite studies, but it is not a good technique for determining if a rock is a meteorite. In proper hands, however, like XRD it would be useful for determining that a rock is not a meteorite because many minerals that occur in terrestrial rocks do not occur in meteorites.

Iron meteorites

If you have found a piece of metal that you think might be an iron meteorite, you need to have it analyzed (at a minimum) for iron (Fe), nickel (Ni), chromium (Cr), and manganese (Mn). A metallurgical lab could do this. Unfortunately, I do not know a lab that does it cheaply. If somebody out there does, please let me know. In proper hands, a handheld XRF analyzer would be useful for iron meteorites.

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