# Density, magnetic susceptibility, and the characterization of ordinary chondrite falls and showers

G. Consolmagno, R. Macke, P. Rochette, D. Britt, J. Gattacceca

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G. Consolmagno, R. Macke, P. Rochette, D. Britt, J. Gattacceca. Density, magnetic susceptibility, and the characterization of ordinary chondrite falls and showers. Meteoritics and Planetary Science, 2006, 41 (3), pp.331-342. 10.1111/j.1945-5100.2006.tb00466.x. hal-03036535

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# Density, magnetic susceptibility, and the characterization of ordinary chondrite falls and showers

G. J. CONSOLMAGNO SJ<fnref n="1" />, R. J. MACKE SJ<fnref n="1" />, <fnref n="2" />, P. ROCHETTE<fnref n="3" />, D. T. BRITT<fnref n="4" />*, and J. GATTACCECA<fnref n="3" />

*(Received 03 November 2005; revision accepted 31 August 2005)*

**Abstract**—Bulk and grain densities of 132 ordinary chondrites from the Vatican Observatory collection were measured and compared with their magnetic susceptibility (for the most part using previously measured values; ten new susceptibility measures were taken for this study). Grain density and magnetic susceptibility combined provide a reliable method of classifying unweathered ordinary chondrites. Unlike traditional chemical tests, this method is fast, nondestructive, and characterizes the whole rock, making it especially appropriate for surveying large collections. The system is less viable for finds; extensive weathering of metallic iron in an H chondrite can cause it to plot among L chondrites, while heavily weathered L chondrites plot among the LL group. This system has revealed outlier stones that may be misclassified meteorites or mislabeled samples; in every case where the magnetic susceptibility of a meteorite does not fit its putative classification, the grain density is also found to be in disagreement in a manner consistent with either severe weathering or misidentification. An analysis of stones from five showers shows that, excluding outliers, these samples tend to cluster tightly within their appropriate groups in a plot of grain versus magnetic susceptibility.

## INTRODUCTION

The classification of ordinary chondrite meteorites into H, L, and LL groups (Van Schmus and Wood 1967) is one of the most useful ways of characterizing and classifying individual meteorites into groups with a common set of characteristics and possibly a common origin. This classification is based on the abundance of metallic iron and the FeO content of the silicate phases, and it has been found that many other characteristics also correlate with meteorite group, ranging from oxygen isotope and trace element abundances to the typical sizes of chondrules and metal grains.

However, to classify an ordinary chondrite, one needs to make a chemical analysis of the meteorite, usually by determining the FeO content in the olivines or pyroxenes either by examining a thin section with a petrographic microscope or by analyzing a polished sample in a microprobe. This carries with it many costs in sample material, resources, and time. First, the meteorite must be cut or broken and a piece removed for a prepared section to be

made, then this section must be polished and coated, and finally it must be examined by a skilled and experienced technician, using elaborate and expensive equipment.

Furthermore, one also has to assume that the sample measured is in fact representative of the whole rock. Most ordinary chondrites are actually breccias and in some cases very different types of material are found to be distributed within the same meteorite. Also, some ordinary chondrites are part of major meteorite showers with large numbers of individual stones that in principle should have identical mineralogy; however, in practice it is very difficult to verify that the mineralogy is in fact uniform, since the process of sectioning and analysis would have to be repeated with each individual sample.

And finally, most meteorites are curated as a partial collection of a large number of fragments held in many different locations around the world. In many cases, only the mass of the meteorite is used to correlate a given sample with its collection's catalogue and to distinguish one sample from another. Ordinary chondrites of differing classes, especially fusion-crusted whole stones, can be hard to tell apart. Errors

<footnote n="1">¹Specola Vaticana, V-00120 Vatican City State</footnote>

<footnote n="2">²Saint Louis University, 3737 Westminster Place, Saint Louis, Missouri 63108-3407, USA</footnote>

<footnote n="3">³Université Aix-Marseille III, CEREGE, BP80, 13545 Aix-en-Provence, France</footnote>

<footnote n="4">⁴Department of Physics, University of Central Florida, P.O. Box 162385, Orlando, Florida 32816-2385, USA</footnote>

<footnote>*Corresponding author. E-mail: britt@physics.ucf.edu</footnote>
<figure><img src="image_3.png" /><figcaption>Fig. 1. Plotted is a representative subset (meteorites for which more than one sample was measured) of the nearly 1000 samples whose magnetic susceptibilities were reported by Rochette et al. (2003). Though H (red), L (blue), and LL (green) have different susceptibility ranges, the ranges do overlap (purples). Each bar is the Log χ range within a meteorite. The solid bars represent 50% of the data; the median value is displayed as a line within the box. The top and bottom of the box mark the limits of ±25% of the population, while the lines extending from the top and bottom of each box indicate the full range of the susceptibilities; outliers (circles) are at least two sigma from the median. The more extreme outliers, circled in brown, may be mislabeled or misclassified samples.</figcaption></figure>

in curation leading to specific pieces being mislabeled are inevitable. But such errors are difficult to spot without a continual, burdensome series of chemical tests.

Given these constraints, the utility of a fast, inexpensive, and nondestructive way of classifying whole samples of ordinary chondrites is obvious. To that end, many workers (e.g., Sugiura 1977 and Nagata 1979) have suggested that a measurement of a meteorite's magnetic properties could serve to classify meteorites. However, most previous attempts have produced unsatisfactory results. For example, magnetic remanence measurements do not provide a unique signature differentiating the various meteorite groups and are subject to spurious results if the sample has previously been exposed to a significant magnetic field, and indeed the strong imposed fields needed in the measurements destroy the original magnetic signature of the sample (Wasilewski and Dickinson 2000).

Recently, however, magnetic susceptibility measurements have been shown to be a much more promising candidate technique (Rochette et al. 2001, 2002, 2003). Magnetic susceptibility is the ratio of the induced magnetization of a material to the strength of a low applied magnetic field (<1 mT). It depends on the capacity of the material to be affected by, or respond to, such a field and is a function of the abundance of the various magnetic phases in the sample, weighed by their specific susceptibility. Rochette et al. (2003) demonstrated that the magnetic susceptibility of unweathered ordinary chondrites is correlated with the amount and oxidation state of the iron within those meteorites. Because these are the primary criteria for the classification of ordinary chondrites into H, L, and LL groups, they suggested that magnetic susceptibility measurements

could be used as a fast and nondestructive tool for meteorite classification.

Figure 1 plots the range of susceptibility measurements taken by Rochette et al. (2003) for a selection of those meteorites where multiple individual pieces were measured. From this figure, one can see that sorting by magnetic susceptibility alone still results in a small overlap among the groups. Though this overlap is limited, and in fact much of it may be the result of misclassified samples rather than a fundamental flaw in the approach itself (one of the advantages of a fast, nondestructive classification is that many more samples can be tested and misidentifications can be spotted), it does raise the concern that, on occasion, susceptibility measurements may lead to an ambiguity in the classification.

Density is another intensive variable that should vary with iron content and oxidation state. The extensive work reviewed by Britt and Consolmagno (2003) indicated that the different classes of ordinary chondrite do have distinctive ranges of densities. Here again, however, there is sufficient overlap among the different classes (especially between L and LL classes) to make one hesitant to use density alone as a definitive characterizer of meteorite type. As with the magnetic susceptibility measurements, this overlap may be due to a number of factors other than the bulk chemistry of the meteorite. Errors or scatter in the density measurements (especially when one attempts to compare measurements made in different laboratories by different techniques on different pieces of the same meteorite), misclassifications or mislabeling of individual samples, and weathering are three important factors that can impede an accurate assessment of meteorites by this method.
<table><caption>Table 1a. H chondrites used in this study.</caption><thead><tr><th>Sample</th><th></th><th>Mass</th><th>Bulk ρ</th><th>+/-</th><th>Grain ρ</th><th>+/-</th><th>Porosity</th><th>+/-</th><th>Log χ</th></tr></thead><tbody><tr><td>Agen</td><td>Fall</td><td>36.82</td><td>3.45</td><td>0.04</td><td>3.77</td><td>0.04</td><td>8.65%</td><td>0.73%</td><td>5.19</td></tr><tr><td>Bath</td><td>Fall</td><td>37.72</td><td>3.53</td><td>0.05</td><td>3.89</td><td>0.04</td><td>9.12%</td><td>0.98%</td><td>5.31</td></tr><tr><td>Burdette</td><td>Find</td><td>18.11</td><td>—</td><td>—</td><td>3.54</td><td>0.04</td><td>—</td><td>—</td><td>5.14</td></tr><tr><td>Cangas de O.</td><td>Fall</td><td>46.75</td><td>3.63</td><td>0.04</td><td>3.82</td><td>0.04</td><td>4.99%</td><td>0.67%</td><td>5.25</td></tr><tr><td>Dimmitt</td><td>Find</td><td>112.72</td><td>—</td><td>—</td><td>3.53</td><td>0.04</td><td>—</td><td>—</td><td>4.88</td></tr><tr><td>Epinal</td><td>Fall</td><td>3.45</td><td>3.50</td><td>0.13</td><td>3.73</td><td>0.05</td><td>6.23%</td><td>3.68%</td><td>5.36</td></tr><tr><td>Forest City</td><td>Fall</td><td>35.76</td><td>3.48</td><td>0.05</td><td>3.77</td><td>0.04</td><td>7.63%</td><td>0.87%</td><td>5.33</td></tr><tr><td>Kernouve</td><td>Fall</td><td>29.69</td><td>3.60</td><td>0.05</td><td>3.77</td><td>0.04</td><td>4.51%</td><td>1.04%</td><td>5.49</td></tr><tr><td>Kernouve</td><td>Fall</td><td>17.96</td><td>3.63</td><td>0.07</td><td>3.74</td><td>0.04</td><td>2.92%</td><td>1.81%</td><td>5.51<sup>a</sup></td></tr><tr><td>Kilbourn</td><td>Fall</td><td>18.72</td><td>—</td><td>—</td><td>3.81</td><td>0.04</td><td>—</td><td>—</td><td>5.29</td></tr><tr><td>Lancon</td><td>Fall</td><td>22.43</td><td>3.74</td><td>0.08</td><td>3.77</td><td>0.04</td><td>0.71%</td><td>1.85%</td><td>5.48</td></tr><tr><td>Le Pressoir</td><td>Fall</td><td>12.73</td><td>—</td><td>—</td><td>3.86</td><td>0.04</td><td>—</td><td>—</td><td>5.53</td></tr><tr><td>Limerick</td><td>Fall</td><td>33.93</td><td>3.67</td><td>0.06</td><td>3.77</td><td>0.04</td><td>2.77%</td><td>1.20%</td><td>5.27</td></tr><tr><td>Mayfield</td><td>Find</td><td>19.30</td><td>3.61</td><td>0.07</td><td>3.61</td><td>0.04</td><td>-0.04%</td><td>1.58%</td><td>5.01</td></tr><tr><td>Menow</td><td>Fall</td><td>29.18</td><td>3.00</td><td>0.05</td><td>3.76</td><td>0.04</td><td>20.22%</td><td>1.16%</td><td>5.46</td></tr><tr><td>Monroe</td><td>Fall</td><td>37.97</td><td>3.66</td><td>0.05</td><td>3.76</td><td>0.04</td><td>2.79%</td><td>0.97%</td><td>5.38</td></tr><tr><td>Monroe</td><td>Fall</td><td>26.78</td><td>3.74</td><td>0.06</td><td>3.77</td><td>0.04</td><td>0.86%</td><td>1.26%</td><td>5.38</td></tr><tr><td>Peekskill</td><td>Fall</td><td>31.84</td><td>—</td><td>—</td><td>3.85</td><td>0.04</td><td>—</td><td>—</td><td>5.13</td></tr><tr><td>Phu Hong</td><td>Fall</td><td>3.98</td><td>3.50</td><td>0.17</td><td>4.15</td><td>0.22</td><td>15.51%</td><td>6.61%</td><td>5.35</td></tr><tr><td>Pipe Creek</td><td>Find</td><td>25.26</td><td>3.41</td><td>0.07</td><td>3.63</td><td>0.04</td><td>5.98%</td><td>1.63%</td><td>5.46</td></tr><tr><td>Quenggouk</td><td>Fall</td><td>51.75</td><td>3.31</td><td>0.04</td><td>3.81</td><td>0.04</td><td>13.25%</td><td>0.71%</td><td>5.34</td></tr><tr><td>Saline</td><td>Find</td><td>30.82</td><td>3.70</td><td>0.06</td><td>3.69</td><td>0.04</td><td>-0.47%</td><td>1.21%</td><td>5.34</td></tr><tr><td>St. Germaine</td><td>Fall</td><td>27.30</td><td>3.40</td><td>0.06</td><td>3.76</td><td>0.04</td><td>9.45%</td><td>1.63%</td><td>5.38</td></tr><tr><td>Thuathe</td><td>Fall</td><td>24.80</td><td>—</td><td>—</td><td>3.84</td><td>0.04</td><td>—</td><td>—</td><td>5.44<sup>a</sup></td></tr><tr><td>Timochin</td><td>Fall</td><td>27.06</td><td>3.39</td><td>0.05</td><td>3.80</td><td>0.04</td><td>10.67%</td><td>0.92%</td><td>5.44</td></tr><tr><td>Toulouse</td><td>Fall</td><td>34.74</td><td>3.73</td><td>0.06</td><td>3.71</td><td>0.04</td><td>-0.51%</td><td>1.40%</td><td>5.29</td></tr><tr><td>Uberaba</td><td>Fall</td><td>24.72</td><td>—</td><td>—</td><td>3.80</td><td>0.04</td><td>—</td><td>—</td><td>5.31</td></tr></tbody></table>

In a series of papers from the Finnish Geological Survey, Kukkonen and Pesonen (1983), Terho et al. (1991, 1993), and Pesonen et al. (1993) first suggested that correlating magnetic susceptibility with density could be a powerful way of resolving these ambiguities. However, their data ultimately showed that a correlation between magnetic susceptibility and bulk density (density that includes the volume of pore spaces within the sample) failed to produce a robust way of separating the different meteorite groups.

One difficulty with the Finnish approach was that bulk densities are strongly affected by differing degrees of porosity. The porosity of ordinary chondrites can range from 0% to 15% (with a few samples showing even higher porosity), which is enough to blur the difference in bulk densities between the different groups of meteorites (Britt and Consolmagno 2003).

More seriously, the Finnish work was done before the intimate link between weathering and density was understood (cf. Bland et al. 1995; Consolmagno et al. 1998, 1999). The terrestrial weathering process fills pore spaces within the meteorite with low-density oxides of metallic iron, which reduces both a meteorite's magnetic susceptibility and grain density (grain density is based on a volume of the rock that excludes pores and voids, but does include the volume of any weathering material filling those voids). As weathering proceeds, the susceptibility and grain density of an H

chondrite is lowered into the range of the L chondrites, while a weathered L chondrite tends to fall into the LL range. Because the Finnish work combined both falls and finds in their analysis and compared these susceptibilities with bulk densities, they were not able to find a definitive separation of different classes by susceptibility and density.

Rochette et al. (2003) achieved a good, if not perfect separation using susceptibility alone by concentrating on falls, not finds, thus eliminating most of the effects of weathering. We demonstrate here that combining those magnetic susceptibility measurements with the grain densities of these unweathered meteorites provides a complete and robust system for the fast, inexpensive, and nondestructive classification of unweathered ordinary chondrite whole meteorite samples.

## THE DATA

For this study, we measured 132 ordinary chondrite samples from the Vatican collection (see Table 1). Of these, 50 came from five meteorite showers, which will be discussed separately in the Grain Density and Magnetic Susceptibility section. The other 82 pieces (from 69 distinct falls) included 26 H chondrites (four finds), 44 L chondrites (14 finds), and 12 LL chondrites (no finds). These samples, without including the shower meteorites, are the ones that we will use

<footnote><sup>a</sup>These magnetic susceptibilities were newly measured for this paper at the University of Aix-Marseille. They are consistent with the 2001 measurements.</footnote>
<table><caption>Table 1b. L chondrites used in this study.</caption><thead><tr><th>Sample</th><th></th><th>Mass</th><th>Bulk ρ</th><th>+/-</th><th>Grain ρ</th><th>+/-</th><th>Porosity</th><th>+/-</th><th>Log χ</th></tr></thead><tbody><tr><td>Ausson</td><td>Fall</td><td>103.13</td><td>—</td><td>—</td><td>3.63</td><td>0.04</td><td>—</td><td>—</td><td>4.99</td></tr><tr><td>Ausson</td><td>Fall</td><td>48.39</td><td>3.31</td><td>0.04</td><td>3.69</td><td>0.04</td><td>10.28%</td><td>0.57%</td><td>4.98</td></tr><tr><td>Barratta</td><td>Find</td><td>88.80</td><td>3.57</td><td>0.04</td><td>3.49</td><td>0.03</td><td>-2.22%</td><td>0.68%</td><td>5.11</td></tr><tr><td>Bath Furnace</td><td>Fall</td><td>43.87</td><td>—</td><td>—</td><td>3.59</td><td>0.04</td><td>—</td><td>—</td><td>4.92</td></tr><tr><td>Bori</td><td>Fall</td><td>23.36</td><td>—</td><td>—</td><td>3.58</td><td>0.04</td><td>—</td><td>—</td><td>5.01</td></tr><tr><td>Chantonnay</td><td>Fall</td><td>25.05</td><td>3.52</td><td>0.06</td><td>3.55</td><td>0.04</td><td>0.70%</td><td>1.55%</td><td>4.90</td></tr><tr><td>Chateau-Renard</td><td>Fall</td><td>46.34</td><td>—</td><td>—</td><td>3.54</td><td>0.04</td><td>—</td><td>—</td><td>5.04</td></tr><tr><td>Claytonville</td><td>Find</td><td>19.16</td><td>—</td><td>—</td><td>3.50</td><td>0.04</td><td>—</td><td>—</td><td>4.54</td></tr><tr><td>Durala</td><td>Fall</td><td>31.80</td><td>3.28</td><td>0.05</td><td>3.62</td><td>0.04</td><td>9.52%</td><td>1.25%</td><td>4.86</td></tr><tr><td>Ergheo</td><td>Fall</td><td>32.68</td><td>3.45</td><td>0.05</td><td>3.49</td><td>0.03</td><td>1.06%</td><td>0.96%</td><td>4.86</td></tr><tr><td>Ergheo</td><td>Fall</td><td>17.30</td><td>3.43</td><td>0.08</td><td>3.50</td><td>0.03</td><td>1.89%</td><td>2.18%</td><td>4.77</td></tr><tr><td>Etter</td><td>Find</td><td>32.72</td><td>—</td><td>—</td><td>3.41</td><td>0.03</td><td>—</td><td>—</td><td>4.72</td></tr><tr><td>Etter</td><td>Find</td><td>24.11</td><td>3.56</td><td>0.07</td><td>3.47</td><td>0.03</td><td>-2.33%</td><td>1.63%</td><td>4.79</td></tr><tr><td>Farmington</td><td>Fall</td><td>108.50</td><td>3.29</td><td>0.08</td><td>3.45</td><td>0.03</td><td>4.49%</td><td>2.06%</td><td>4.83</td></tr><tr><td>Garraf</td><td>Find</td><td>17.90</td><td>—</td><td>—</td><td>3.56</td><td>0.04</td><td>—</td><td>—</td><td>4.69</td></tr><tr><td>Grossliebenthal</td><td>Fall</td><td>21.30</td><td>—</td><td>—</td><td>3.57</td><td>0.04</td><td>—</td><td>—</td><td>4.71</td></tr><tr><td>Grossliebenthal</td><td>Fall</td><td>19.90</td><td>—</td><td>—</td><td>3.62</td><td>0.04</td><td>—</td><td>—</td><td>4.68</td></tr><tr><td>Homestead</td><td>Fall</td><td>29.66</td><td>3.45</td><td>0.05</td><td>3.61</td><td>0.04</td><td>4.29%</td><td>0.99%</td><td>5.18</td></tr><tr><td>Honolulu</td><td>Fall</td><td>101.25</td><td>—</td><td>—</td><td>3.62</td><td>0.04</td><td>—</td><td>—</td><td>4.78</td></tr><tr><td>Kendleton</td><td>Fall</td><td>121.15</td><td>—</td><td>—</td><td>3.57</td><td>0.04</td><td>—</td><td>—</td><td>4.87</td></tr><tr><td>Kermichel</td><td>Find</td><td>61.14</td><td>—</td><td>—</td><td>3.45</td><td>0.03</td><td>—</td><td>—</td><td>4.08</td></tr><tr><td>Kermichel</td><td>Find</td><td>37.66</td><td>3.35</td><td>0.07</td><td>3.44</td><td>0.03</td><td>2.70%</td><td>1.78%</td><td>3.98<sup>a</sup></td></tr><tr><td>Kyushu</td><td>Fall</td><td>42.60</td><td>3.42</td><td>0.05</td><td>3.60</td><td>0.04</td><td>5.07%</td><td>0.98%</td><td>4.89</td></tr><tr><td>Lakewood</td><td>Find</td><td>26.71</td><td>—</td><td>—</td><td>3.43</td><td>0.04</td><td>—</td><td>—</td><td>4.50</td></tr><tr><td>Long Island</td><td>Find</td><td>41.42</td><td>3.51</td><td>0.05</td><td>3.51</td><td>0.04</td><td>-0.05%</td><td>0.90%</td><td>4.32</td></tr><tr><td>Marion (Iowa)</td><td>Fall</td><td>30.65</td><td>3.27</td><td>0.04</td><td>3.64</td><td>0.04</td><td>10.06%</td><td>0.65%</td><td>4.74</td></tr><tr><td>Marmande</td><td>Fall</td><td>24.88</td><td>—</td><td>—</td><td>3.63</td><td>0.04</td><td>—</td><td>—</td><td>4.95</td></tr><tr><td>McKinney</td><td>Find</td><td>96.21</td><td>3.37</td><td>0.10</td><td>3.52</td><td>0.04</td><td>4.29%</td><td>2.66%</td><td>4.75</td></tr><tr><td>McKinney</td><td>Find</td><td>35.60</td><td>3.56</td><td>0.11</td><td>3.53</td><td>0.04</td><td>-0.96%</td><td>3.00%</td><td>4.69</td></tr><tr><td>Nerft</td><td>Fall</td><td>39.61</td><td>3.47</td><td>0.05</td><td>3.64</td><td>0.04</td><td>4.54%</td><td>0.97%</td><td>5.16</td></tr><tr><td>Ness County</td><td>Find</td><td>31.72</td><td>3.33</td><td>0.05</td><td>3.53</td><td>0.04</td><td>5.63%</td><td>1.12%</td><td>4.21</td></tr><tr><td>New Concord</td><td>Fall</td><td>63.70</td><td>—</td><td>—</td><td>3.64</td><td>0.04</td><td>—</td><td>—</td><td>5.01</td></tr><tr><td>Pavlograd</td><td>Fall</td><td>40.87</td><td>3.38</td><td>0.06</td><td>3.63</td><td>0.04</td><td>6.75%</td><td>1.33%</td><td>4.77</td></tr><tr><td>Pricetown</td><td>Fall</td><td>30.19</td><td>3.24</td><td>0.05</td><td>3.64</td><td>0.04</td><td>10.85%</td><td>1.19%</td><td>4.82</td></tr><tr><td>Quincay</td><td>Fall</td><td>29.44</td><td>3.49</td><td>0.05</td><td>3.56</td><td>0.04</td><td>1.94%</td><td>1.10%</td><td>4.74</td></tr><tr><td>Sevrukovo</td><td>Fall</td><td>19.90</td><td>—</td><td>—</td><td>3.54</td><td>0.04</td><td>—</td><td>—</td><td>4.89</td></tr><tr><td>St. Chris.-le-Char.</td><td>Fall</td><td>38.81</td><td>3.45</td><td>0.05</td><td>3.63</td><td>0.04</td><td>5.02%</td><td>0.90%</td><td>4.92</td></tr><tr><td>St. Michel</td><td>Fall</td><td>38.77</td><td>3.45</td><td>0.04</td><td>3.62</td><td>0.04</td><td>4.69%</td><td>0.83%</td><td>4.75</td></tr><tr><td>St. Michel</td><td>Fall</td><td>32.42</td><td>3.51</td><td>0.05</td><td>3.65</td><td>0.04</td><td>4.00%</td><td>1.08%</td><td>4.95</td></tr><tr><td>Tadjera</td><td>Fall</td><td>31.42</td><td>3.70</td><td>0.06</td><td>3.51</td><td>0.04</td><td>-5.37%</td><td>1.42%</td><td>5.00</td></tr><tr><td>Tenham</td><td>Fall</td><td>20.75</td><td>3.46</td><td>0.07</td><td>3.55</td><td>0.04</td><td>2.63%</td><td>1.68%</td><td>4.75</td></tr><tr><td>Tourin.-la-Grosse</td><td>Fall</td><td>45.34</td><td>3.36</td><td>0.04</td><td>3.64</td><td>0.04</td><td>7.62%</td><td>0.75%</td><td>5.01</td></tr><tr><td>Waconda</td><td>Find</td><td>126.01</td><td>—</td><td>—</td><td>3.61</td><td>0.04</td><td>—</td><td>—</td><td>4.76</td></tr><tr><td>Waconda</td><td>Find</td><td>26.67</td><td>—</td><td>—</td><td>3.71</td><td>0.04</td><td>—</td><td>—</td><td>4.89</td></tr></tbody></table>

to define and test the classification of meteorites by density and susceptibility.

The masses of these samples ranged from 3 g to 128 g. The measuring apparatus limited the sizes of the samples that could be measured. The container size of the pycnometer and (in the case of some H chondrites) the saturation of the large coil (8 cm) alternating field bridge KLY-2 device used to measure magnetic susceptibility put an upper limit on the size of the samples that could be measured. Accurate

measurements were especially problematic for the smallest samples. Bulk densities were difficult to obtain for samples smaller than 10 g; 30 of the 82 samples could not be measured accurately for bulk density and so no porosity could be calculated for them. Two groups of Holbrook pieces (most of them smaller than 2 g) were gathered and measured as a group rather than as individual stones.

The bulk density was found with the glass beads method (Consolmagno and Britt 1998; Wilkison et al. 2003) and grain

<footnote><sup>a</sup>These magnetic susceptibilities were newly measured for this paper at the University of Aix-Marseille. They are consistent with the 2001 measurements.</footnote>
<table><caption>Table 1c. LL chondrites used in this study.</caption><thead><tr><th>Sample</th><th></th><th>Mass</th><th>Bulk ρ</th><th>+/-</th><th>Grain ρ</th><th>+/-</th><th>Porosity</th><th>+/-</th><th>Log χ</th></tr></thead><tbody><tr><td>Bandong</td><td>Fall</td><td>24.87</td><td>—</td><td>—</td><td>3.59</td><td>0.04</td><td>—</td><td>—</td><td>3.87</td></tr><tr><td>Dhurmsala</td><td>Fall</td><td>85.80</td><td>—</td><td>—</td><td>3.56</td><td>0.04</td><td>—</td><td>—</td><td>4.24<sup>a</sup></td></tr><tr><td>Dhurmsala</td><td>Fall</td><td>29.28</td><td>3.31</td><td>0.05</td><td>3.54</td><td>0.04</td><td>6.31%</td><td>1.14%</td><td>4.33</td></tr><tr><td>Ensisheim</td><td>Fall</td><td>33.55</td><td>3.40</td><td>0.05</td><td>3.53</td><td>0.04</td><td>3.74%</td><td>1.11%</td><td>4.08</td></tr><tr><td>Jelica</td><td>Fall</td><td>127.70</td><td>—</td><td>—</td><td>3.50</td><td>0.03</td><td>—</td><td>—</td><td>3.52</td></tr><tr><td>Mangwendi</td><td>Fall</td><td>92.20</td><td>3.15</td><td>0.07</td><td>3.62</td><td>0.04</td><td>13.12%</td><td>2.07%</td><td>4.16</td></tr><tr><td>Parnallee</td><td>Fall</td><td>89.00</td><td>3.29</td><td>0.04</td><td>3.52</td><td>0.04</td><td>6.56%</td><td>0.74%</td><td>4.46</td></tr><tr><td>Parnallee</td><td>Fall</td><td>5.60</td><td>—</td><td>—</td><td>3.51</td><td>0.04</td><td>—</td><td>—</td><td>4.49</td></tr><tr><td>Parnallee</td><td>Fall</td><td>3.85</td><td>—</td><td>—</td><td>3.50</td><td>0.05</td><td>—</td><td>—</td><td>4.61<sup>a</sup></td></tr><tr><td>Savtschenskoje</td><td>Fall</td><td>14.94</td><td>3.36</td><td>0.08</td><td>3.62</td><td>0.04</td><td>7.16%</td><td>2.27%</td><td>4.32</td></tr><tr><td>Soko Banja</td><td>Fall</td><td>27.16</td><td>3.17</td><td>0.05</td><td>3.58</td><td>0.04</td><td>11.37%</td><td>1.30%</td><td>4.29</td></tr><tr><td>Vavilovka</td><td>Fall</td><td>26.50</td><td>—</td><td>—</td><td>3.52</td><td>0.04</td><td>—</td><td>—</td><td>3.66</td></tr></tbody></table>

densities were measured using a Quantochrome Ultrapycnometer. All of the density measurements were taken during July 2004.

The magnetic susceptibility of most of these samples had previously been measured (Rochette et al. 2003) over a period of three days in early 2001. To complete these measurements, ten samples missed at that time were measured using the same equipment at the Université Aix-Marseille in late 2004 and early 2005. As described by Rochette et al. (2001), the instrument used was an alternating field (AF) bridge KLY-2 from Agico, Brno, operating at a frequency of 920 Hz with a magnetic induction of 0.4 mT, calibrated before each measurement session using a standard provided by Agico. They reported that the most serious source of scatter in their measurements was the anisotropy of the susceptibility in the samples; only one arbitrary orientation was used to produce the χ values reported, although ultimately their measuring procedure involved averaging two or three measurements in different orientations. Based on such measurements and the modeling reported in Rochette et al. (2001), they concluded that for the range of susceptibilities seen in ordinary chondrites, the error in log χ due to shape (except for extreme cases such as thin slabs) or the orientation of grains is less than 0.1 (in log χ).

Though negligible for the purposes of this paper, we note that the magnetic susceptibility anisotropy can be a valuable tool for exploring the petrofabric of meteorites, as reported in Gattacceca et al. 2005.

The helium pycnometer used for the grain density measurements automatically took twenty measures and reported the average of the last five; the formal error in this procedure was generally ±0.04 g/cm³ with the largest component of this uncertainty being the ±0.01 g precision in the sample mass. In fact, in a few cases, the same sample was remeasured after several days, and results within 0.05 g/cm³ were generally found; however, larger variations were found for the smallest samples. Bulk density measurements are the average of at least ten measures; the error in the bulk density was larger, generally in the range of 0.05 to 0.1 g/cm³. As

reported by Rochette et al. (2003), the precision of the magnetic susceptibility measurements was better than 0.01 (in log c, where c has units of 10⁻⁹ m³/kg).

Note that the density and susceptibility measurements for all the meteorite samples were performed in a completely consistent manner, by the same people using the same equipment in the same way over a short period of time, ensuring that all samples were handled in as common a fashion as possible and eliminating one possible source of variation within the data.

## GRAIN DENSITY AND MAGNETIC SUSCEPTIBILITY

The correlation between grain density, magnetic susceptibility, and meteorite type in our data set is illustrated in Fig. 2. Note that there is an overlap in density between L and LL meteorites in our sample, as well as a small overlap in susceptibility between the H and L meteorites, but by using both susceptibility and grain density together, these ambiguities are resolved.

Exceptions to these striking divisions can be clues to meteorite misclassifications. Indeed, perhaps the greatest utility in the combined use of density and susceptibility measurements is that an anomalous value in one measure can be confirmed by looking for an anomaly in the other measure.

One example is Le Pressoir (a meteorite circled in Fig. 1). Classified in Grady (2000) as an L chondrite (based on optical work done in the 1960s), it has both a magnetic susceptibility and grain density completely consistent with an H chondrite. A re-examination of this meteorite by Rochette et al. (2003) using a microprobe indicated that it was previously misclassified; it is in fact an H, and is so plotted (among the H chondrites, shown as squares) in Fig. 2. Rochette et al. (2003) also describe other examples of misclassifications uncovered by the magnetic susceptibility measurements.

By contrast, other anomalies in our data are probably due to measurement difficulties and not misclassifications. As seen in Table 1, two meteorites in our sample lie at the

<footnote><sup>a</sup>These magnetic susceptibilities were newly measured for this paper at the University of Aix-Marseille. They are consistent with the 2001 measurements.</footnote>
<table><caption>Table 1d. Shower meteorites used in this study.</caption><thead><tr><th>Sample</th><th>Mass</th><th>Bulk ρ</th><th>+/-</th><th>Grain ρ</th><th>+/-</th><th>Porosity</th><th>+/-</th><th>Log χ</th></tr></thead><tbody><tr><td rowspan="10">Pultusk (H)</td><td>20.00</td><td>3.70</td><td>0.08</td><td>3.71</td><td>0.04</td><td>0.27%</td><td>1.86%</td><td>5.37</td></tr><tr><td>19.90</td><td>3.80</td><td>0.07</td><td>3.81</td><td>0.04</td><td>0.17%</td><td>1.60%</td><td>5.28</td></tr><tr><td>13.00</td><td>3.76</td><td>0.08</td><td>3.77</td><td>0.04</td><td>0.38%</td><td>2.04%</td><td>5.42</td></tr><tr><td>9.36</td><td>3.45</td><td>0.07</td><td>3.50</td><td>0.04</td><td>1.34%</td><td>1.92%</td><td>4.74</td></tr><tr><td>8.45</td><td>3.36</td><td>0.07</td><td>3.80</td><td>0.09</td><td>11.55%</td><td>2.63%</td><td>5.45</td></tr><tr><td>8.35</td><td>3.66</td><td>0.10</td><td>3.81</td><td>0.04</td><td>3.84%</td><td>2.63%</td><td>5.28</td></tr><tr><td>8.18</td><td>3.22</td><td>0.07</td><td>3.55</td><td>0.04</td><td>9.19%</td><td>2.02%</td><td>4.57</td></tr><tr><td>8.13</td><td>3.75</td><td>0.11</td><td>3.79</td><td>0.04</td><td>1.03%</td><td>2.67%</td><td>5.25</td></tr><tr><td>8.21</td><td>3.57</td><td>0.09</td><td>3.81</td><td>0.04</td><td>6.26%</td><td>2.22%</td><td>5.40</td></tr><tr><td>5.82</td><td>3.36</td><td>0.10</td><td>3.82</td><td>0.05</td><td>11.97%</td><td>3.02%</td><td>5.32</td></tr><tr><td>4.77</td><td>3.56</td><td>0.14</td><td>3.78</td><td>0.10</td><td>5.72%</td><td>4.36%</td><td>5.39</td></tr><tr><td rowspan="17">Holbrook<sup>a</sup> (L)</td><td>77.70</td><td>3.37</td><td>0.05</td><td>3.62</td><td>0.04</td><td>7.23%</td><td>0.49%</td><td>4.72</td></tr><tr><td>53.80</td><td>3.48</td><td>0.03</td><td>3.78</td><td>0.04</td><td>7.84%</td><td>0.58%</td><td>4.67</td></tr><tr><td>49.50</td><td>3.34</td><td>0.03</td><td>3.63</td><td>0.04</td><td>8.39%</td><td>1.08%</td><td>4.72</td></tr><tr><td>40.50</td><td>3.33</td><td>0.05</td><td>3.63</td><td>0.04</td><td>8.52%</td><td>1.10%</td><td>4.69</td></tr><tr><td>34.60</td><td>3.51</td><td>0.05</td><td>3.52</td><td>0.04</td><td>0.26%</td><td>0.97%</td><td>4.38</td></tr><tr><td>33.80</td><td>3.32</td><td>0.04</td><td>3.64</td><td>0.04</td><td>8.85%</td><td>1.00%</td><td>4.65</td></tr><tr><td>27.10</td><td>3.43</td><td>0.06</td><td>3.70</td><td>0.04</td><td>7.46%</td><td>1.58%</td><td>4.72</td></tr><tr><td>24.70</td><td>3.45</td><td>0.06</td><td>3.62</td><td>0.04</td><td>4.74%</td><td>1.37%</td><td>4.67<sup>b</sup></td></tr><tr><td>23.90</td><td>3.36</td><td>0.05</td><td>3.66</td><td>0.04</td><td>8.44%</td><td>0.95%</td><td>4.67<sup>b</sup></td></tr><tr><td>21.30</td><td>3.41</td><td>0.03</td><td>3.72</td><td>0.04</td><td>7.87%</td><td>0.90%</td><td>4.75</td></tr><tr><td>18.10</td><td>3.52</td><td>0.04</td><td>3.57</td><td>0.04</td><td>1.38%</td><td>1.12%</td><td>4.23</td></tr><tr><td>9.14</td><td>3.36</td><td>0.05</td><td>3.67</td><td>0.04</td><td>9.56%</td><td>2.33%</td><td>4.67</td></tr><tr><td>7.27</td><td>3.46</td><td>0.08</td><td>3.64</td><td>0.05</td><td>5.50%</td><td>2.51%</td><td>4.68</td></tr><tr><td>4.20</td><td>3.28</td><td>0.15</td><td>3.69</td><td>0.05</td><td>11.07%</td><td>4.76%</td><td>4.78</td></tr><tr><td>3.60</td><td>3.28</td><td>0.15</td><td>3.69</td><td>0.05</td><td>11.07%</td><td>4.76%</td><td>4.78</td></tr><tr><td>1.83</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>2.23%</td><td>4.63</td></tr><tr><td>1.66</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>2.41%</td><td>4.63</td></tr><tr><td>1.56</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>2.53%</td><td>4.63</td></tr><tr><td>1.55</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>2.54%</td><td>4.63</td></tr><tr><td>1.30</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>2.95%</td><td>4.63</td></tr><tr><td>1.26</td><td>3.52</td><td>0.04</td><td>3.67</td><td>0.04</td><td>4.09%</td><td>3.03%</td><td>4.63</td></tr><tr><td>0.50</td><td>3.28</td><td>0.15</td><td>3.69</td><td>0.05</td><td>11.07%</td><td>4.76%</td><td>4.78</td></tr><tr><td rowspan="6">Mocs (L)</td><td>101.94</td><td>3.36</td><td>0.04</td><td>3.66</td><td>0.04</td><td>8.32%</td><td>0.71%</td><td>4.92</td></tr><tr><td>100.85</td><td>3.29</td><td>0.04</td><td>3.65</td><td>0.04</td><td>9.67%</td><td>0.50%</td><td>4.85</td></tr><tr><td>74.40</td><td>3.37</td><td>0.04</td><td>3.66</td><td>0.04</td><td>7.86%</td><td>0.63%</td><td>4.87</td></tr><tr><td>66.20</td><td>3.39</td><td>0.04</td><td>3.68</td><td>0.04</td><td>7.68%</td><td>0.75%</td><td>4.81</td></tr><tr><td>55.38</td><td>3.32</td><td>0.04</td><td>3.70</td><td>0.04</td><td>10.38%</td><td>0.86%</td><td>4.83</td></tr><tr><td>36.40</td><td>3.31</td><td>0.04</td><td>3.63</td><td>0.04</td><td>8.79%</td><td>0.84%</td><td>4.92</td></tr><tr><td rowspan="4">L'Aigle (L)</td><td>22.34</td><td>3.31</td><td>0.06</td><td>3.69</td><td>0.04</td><td>10.19%</td><td>1.37%</td><td>4.90</td></tr><tr><td>52.02</td><td>3.63</td><td>0.04</td><td>3.78</td><td>0.04</td><td>3.90%</td><td>0.56%</td><td>5.36</td></tr><tr><td>48.77</td><td>3.43</td><td>0.04</td><td>3.44</td><td>0.03</td><td>0.43%</td><td>0.64%</td><td>4.48</td></tr><tr><td>24.14</td><td>3.40</td><td>0.05</td><td>3.66</td><td>0.04</td><td>7.21%</td><td>1.12%</td><td>4.94</td></tr><tr><td rowspan="2">Knyahinya (L/LL)</td><td>19.50<sup>c</sup></td><td>—</td><td>—</td><td>3.70</td><td>0.10</td><td>—</td><td>—</td><td>—</td></tr><tr><td>9.44</td><td>3.35</td><td>0.08</td><td>3.71</td><td>0.04</td><td>9.57%</td><td>2.20%</td><td>4.96</td></tr><tr><td rowspan="4">Knyahinya (L/LL)</td><td>60.44</td><td>3.39</td><td>0.08</td><td>3.50</td><td>0.04</td><td>3.10%</td><td>2.25%</td><td>4.70</td></tr><tr><td>45.40</td><td>3.47</td><td>0.05</td><td>3.51</td><td>0.04</td><td>1.14%</td><td>0.92%</td><td>4.58</td></tr><tr><td>27.19</td><td>3.53</td><td>0.04</td><td>3.54</td><td>0.04</td><td>0.38%</td><td>0.79%</td><td>4.71<sup>b</sup></td></tr><tr><td>9.65</td><td>3.63</td><td>0.10</td><td>3.77</td><td>0.04</td><td>3.73%</td><td>2.69%</td><td>5.35<sup>b</sup></td></tr><tr><td></td><td>9.42</td><td>3.62</td><td>0.16</td><td>3.54</td><td>0.04</td><td>-2.25%</td><td>4.25%</td><td>4.76<sup>b</sup></td></tr></tbody></table>

<footnote><sup>a</sup>The smallest samples of Holbrook, shown in italics, were measured in two groups and not as individual samples.</footnote>

<footnote><sup>b</sup>These magnetic susceptibilities were newly measured for this paper at the University of Aix-Marseille. They are consistent with the 2001 measurements.</footnote>

<footnote><sup>c</sup>This sample, no longer part of the Vatican collection, was measured for grain density with the other samples in 2004, to confirm that its density is consistent with other L'Aigle L chondrites.</footnote>
<table><caption>Table 1e. Non-ordinary chondrite meteorites measured in this study.</caption><thead><tr><th>Sample</th><th>Type</th><th>Mass</th><th>Bulk ρ</th><th>+/-</th><th>Grain ρ</th><th>+/-</th><th>Porosity</th><th>+/-</th><th>Log χ</th></tr></thead><tbody><tr><td colspan="10"><strong>Carbonaceous meteorites</strong></td></tr><tr><td>Lancé</td><td>CO</td><td>7.58</td><td>3.5</td><td>0.2</td><td>3.76</td><td>0.04</td><td>7%</td><td>5%</td><td>4.35</td></tr><tr><td>Ornans</td><td>CO</td><td>25.26</td><td>2.36</td><td>0.06</td><td>3.7</td><td>0.04</td><td>36%</td><td>2%</td><td>4.29</td></tr><tr><td>Renazzo</td><td>CR</td><td>12.15</td><td>3.42</td><td>0.1</td><td>3.51</td><td>0.04</td><td>3%</td><td>3%</td><td>5.10</td></tr><tr><td>Allende</td><td>CV</td><td>167.23</td><td>2.92</td><td>0.06</td><td>3.84</td><td>0.08</td><td>24%</td><td>3%</td><td>3.56</td></tr><tr><td>Vigarano</td><td>CV</td><td></td><td></td><td></td><td>3.54</td><td>0.04</td><td></td><td></td><td>4.39<sup>a</sup></td></tr><tr><td colspan="10"><strong>Achondrites</strong></td></tr><tr><td>Bishopville</td><td>Aubrite</td><td>4.3</td><td>2.95</td><td>0.1</td><td>3.46</td><td>0.04</td><td>15%</td><td>3%</td><td>3.04</td></tr><tr><td>Cumberland Falls</td><td>Aubrite</td><td>23.34</td><td></td><td></td><td>3.29</td><td>0.04</td><td></td><td></td><td>3.93</td></tr><tr><td>Peña Blanca Springs</td><td>Aubrite</td><td>30.57</td><td></td><td></td><td>3.14</td><td>0.04</td><td></td><td></td><td>2.93</td></tr><tr><td>Dar al Gani 411</td><td>Eucrite</td><td>19.32</td><td></td><td></td><td>3.32</td><td>0.04</td><td></td><td></td><td>2.98</td></tr><tr><td>Jonzac</td><td>Eucrite</td><td>31.85</td><td></td><td></td><td>3.25</td><td>0.04</td><td></td><td></td><td>2.64</td></tr><tr><td>Juvinas</td><td>Eucrite</td><td>70.93</td><td>3.13</td><td>0.06</td><td>3.2</td><td>0.04</td><td>2%</td><td>2%</td><td>2.89</td></tr><tr><td>Stannern</td><td>Eucrite</td><td>18.3</td><td></td><td></td><td>3.33</td><td>0.04</td><td></td><td></td><td>2.65</td></tr><tr><td>Roda</td><td>Diogenite</td><td>7.61</td><td></td><td></td><td>3.53</td><td>0.04</td><td></td><td></td><td>3.00</td></tr><tr><td>Shalka</td><td>Diogenite</td><td>18.32</td><td></td><td></td><td>3.49</td><td>0.04</td><td></td><td></td><td>2.99</td></tr><tr><td>Chassigny</td><td>SNC</td><td>15.66</td><td>3.5</td><td>0.1</td><td>3.77</td><td>0.04</td><td>7%</td><td>3%</td><td>2.98</td></tr></tbody></table>

boundaries of their groups. Phu Hong has an anomalously high grain density (4.15 ± 0.22 g/cm³, higher than any other H meteorite we have measured) while one sample of Parnallee, an LL, plots very close to the L group in magnetic susceptibility and significantly far from the other two Parnallee samples. We note that both it and the Parnallee sample are at the lower range of our size range (each less than 4 g) and we suspect that their slightly anomalous values may be the result of measurement error. In fact, we attempted the density measurement of Phu Hong three times with the resulting large uncertainty listed in Table 1 (Phu Hong plots outside the bounds of Fig. 2, but the lower end of its error bar would in fact lie at the upper edge of the H region.). An inhomogeneous distribution of iron within the meteorite sample is another a possible explanation for these anomalous results; again, the small sizes of the samples would be consistent with such an inhomogeneity. This sort of scatter is discussed in greater detail below when we compare the measurements of meteorites from showers.

One can use portable and relatively inexpensive equipment to make magnetic susceptibility measurements. Accurate grain density measurements, however, require a somewhat more elaborate laboratory setup. By contrast, it is much simpler to make bulk density measurements using glass beads or other Archimedian fluids (Among other fluids— including water—alcohol and carbon tetrachloride have been used for samples where one is not too worried about possible contamination issues. Care must be taken to prevent significant entry of the fluids into pore spaces.). Thus, it is useful to see if bulk density instead of grain density could serve to classify meteorite groups.

A plot similar to Fig. 2 but using bulk densities is shown in Fig. 3. As can be seen, there is almost a complete overlap in

bulk densities among the three meteorite groups, and so bulk density contributes no useful discrimination among them. The separation visible in Fig. 3 is due entirely to the differences in magnetic susceptibility among the groups already noted by Rochette et al. (2003). There remains the small overlap between L and H groups that only grain density, not bulk density, can resolve.

All the points in Figs. 2 and 3 are falls. Finds present a more serious problem. As can be seen in Fig. 4, the sorting is less definitive and H or L finds can be confused for L or LL falls. It remains possible that an independent measure of weathering could be applied to help resolve this ambiguity, but the how this modeling could be done remains for future work.

Unfortunately, for the moment, this difficulty limits the utility of using this method as a definitive way to classify the large number of dry desert finds entering our collections. Nonetheless, a density and magnetic susceptibility screening of these meteorites can provide at least a preliminary classification. Since weathering works in only one direction, one can obviously say that any find that plots within the H region is indeed an H; there is an ambiguity only for those plotting in the L and LL regions. On the other hand, it would be interesting to plot a similarly large sample of dry desert or Antarctic finds to see if there is a sorting of the meteorite groups into distinct ranges of density and susceptibility among them, perhaps as well defined as those seen in Fig. 2, but with different ranges of density and susceptibility.

## CONSISTENCY WITHIN SHOWERS

In addition to the measurements made of one or two samples from 69 different falls noted in the Grain Density and

<footnote><sup>a</sup>Based on two different samples; density from 81.8 g sample, magnetic susceptibility from 20.89 g sample.</footnote>
<figure><img src="image_4.png" /><figcaption>Fig. 2. Magnetic susceptibility versus grain density for falls. The susceptibility is presented as Log χ where χ has units of 10⁻⁹ m³/kg. Density is given in units of g/cm³ = 10³ kg/m³.</figcaption></figure>

Magnetic Susceptibility section, we also measured multiple samples of five meteorites that fell as showers. These were the H chondrite, Pultusk, the L chondrites Holbrook, L'Aigle, and Mocs, and the L/LL chondrite, Knyahinya. Most of the samples measured were whole or nearly whole fusion-crusted stones. As seen in Fig. 5, each meteorite's samples cluster within their appropriate class. Note that the samples of the meteorite Knyahinya, classified as an intermediate L/LL type, plot directly between the L and LL groups.

However, every shower except Mocs shows one or two discordant samples. In total, seven of the 50 samples measured do not plot with the other stones of their shower. For all the showers except L'Aigle (where two of the four stones were discordant, and so a tight average is not available), these samples lie at least two standard deviations from the uncorrected average of their shower in density or susceptibility. These include two discordant stones each from Holbrook, L'Aigle, and Pultusk, and one sample of Knyahinya. But in every case, a discordant sample in susceptibility was also discordant in density in a way consistent with weathering or mislabeling.

Holbrook is a meteorite with a complex collection history; some pieces were collected soon after the meteorite fell, while others were recovered from the Arizona desert many years after the fall. Thus one should not be surprised at differing degrees of weathering among the samples. The two discordant samples of this L chondrite do in fact appear to plot in the same region as the L finds in Fig. 3. In addition, the two discordant samples have essentially zero porosity (0.3% ± 1% and 1.4% ± 1.2%) whereas the average porosity of the

<figure><img src="image_5.png" /><figcaption>Fig. 3. Susceptibility versus bulk density for falls. Note where the open square L meteorites plot amid, and even atop, solid squares of the H meteorites. Bulk density fails to separate the classes.</figcaption></figure>

other samples of Holbrook is 7.2% ± 2.6% (Throughout this paper, the quoted errors for an individual sample are the formal measurement error; those for an average of many samples are the standard deviation of the average.). Thus we conclude that the two discordant Holbrook samples are significantly more weathered than the rest of the group, explaining why their values of density and susceptibility do not match the others from this shower.

The case of Pultusk is not as clear-cut. Again the two samples that are discrepant in susceptibility are also mismatched in grain density, plotting what should be H samples among the L group (but near the LL group). However, a wide range of porosities, from zero to 12%, is seen among all of the Pultusk samples, and the two discordant samples' porosities are 0% and 9%. It is possible that the zero porosity sample is a weathered piece of Pultusk. However, other low-porosity samples of Pultusk are not discordant, and the other discordant sample has a high porosity. It is therefore more likely that these are mislabeled meteorites accidentally mixed into the Pultusk samples. There is no obvious visible difference in appearance between these two stones and the other Pultusk samples.

The one discordant sample of Knyahinya has an unusually high grain density of 3.77 ± 0.04 g/cm³ (the average of the other four samples is 3.52 ± 0.02 g/cm³) and also an anomalously large log χ value of 5.35, indicating that this piece may be a misidentified H meteorite. Indeed it is
<figure><img src="image_6.png" /><figcaption>Fig. 4. Susceptibility versus grain density for finds. The arrows show the trends caused by weathering, as H finds move into the L field and Ls into the LL field.</figcaption></figure>

interesting to note that this H-like “Knyahinya” has a mass of about 9.5 g, which is the same mass as one of the discordant L/LL-like “Pultusk” pieces. It is quite conceivable that these two pieces have simply been inadvertently exchanged at some time in the 100 year history of the Vatican meteorite collection.

L'Aigle presents the most puzzling situation. Of the five samples measured for grain density (one piece, no longer part of the collection, does not have a magnetic susceptibility measurement), three have appropriate grain densities and (for the two that were measured) magnetic susceptibilities for an L chondrite. One discordant L'Aigle sample lies in the LL region, but as with Holbrook it could simply be a very weathered stone; its porosity is essentially zero (0.4% ± 0.6%), which is typical of a find, while the average porosity of the three “normal” samples is 8.4% ± 1.7%. However, the fifth sample measured plots firmly in the H chondrite region. With a mass of 52 g, its size is typical of the samples measured here; there is no reason to suspect a large measurement error. This is almost certainly a misidentified meteorite.

The odd thing is that this stone is also one of the
collection's best-documented samples. With this meteorite is
a tag in French labeling it as a sample "tombée à l'Aigle dept.
de L'Orme le 16. floréal an 11" (fallen at L'Aigle, dept. of
L'Orme, on the 16th of Floréal in the year 11); below this
writing is a notation in pencil "52 g." The use of the French
Revolution's calendar month and year suggests that this
document is a near-contemporary of the fall, while the mass
connects this tag with the sample in question. There is also an
undated but apparently nineteenth-century tag identifying a

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5. Meteorite showers tend to plot into tighter populations than the groups to which they belong. a) Pultusk, Holbrook, and Knyahinya. The discordant Knyahinya piece plots among the Pultusk pieces, while the discordant Pultusk pieces plot amid Knyahinya. The discordant Holbrook pieces plot where heavily weathered L finds are seen to plot in Fig. 4. b) Mocs and L'Aigle. All of the pieces of Mocs are tightly clustered, while two of the four L'Aigle pieces are not; the one among the H meteorites is probably a misidentification.</figcaption></figure>

52 g sample of L'Aigle from the mineral dealer, H. Minod,
Comptoir Mineralogique et Geologique Suisse, of Geneva;
presumably he was the source of the meteorite in the original
nineteenth-century collection of the Marquis de Mauroy, from
which the Vatican collection is derived (Consolmagno,
Forthcoming). If this is indeed a misidentified H chondrite,
when did the mix-up occur? The only other ordinary
<table><caption>Table 2. Spread in groups and showers.</caption><thead><tr><th></th><th>Number</th><th>Grain ρ</th><th>+/-</th><th>Bulk ρ</th><th>+/-</th><th>Log χ</th><th>+/-</th></tr></thead><tbody><tr><td>H falls</td><td>22</td><td>3.80</td><td>0.09</td><td>3.53</td><td>0.19</td><td>5.36</td><td>0.10</td></tr><tr><td>L falls</td><td>31</td><td>3.59</td><td>0.06</td><td>3.42</td><td>0.11</td><td>4.89</td><td>0.13</td></tr><tr><td>LL falls</td><td>12</td><td>3.55</td><td>0.04</td><td>3.28</td><td>0.10</td><td>4.17</td><td>0.33</td></tr><tr><td>All data</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Pultusk</td><td>11</td><td>3.74</td><td>0.11</td><td>3.56</td><td>0.19</td><td>5.22</td><td>0.29</td></tr><tr><td>Holbrook</td><td>22</td><td>3.66</td><td>0.05</td><td>3.42</td><td>0.09</td><td>4.65</td><td>0.13</td></tr><tr><td>L'Aigle</td><td>5</td><td>3.66</td><td>0.13</td><td>3.45</td><td>0.12</td><td>4.94</td><td>0.36</td></tr><tr><td>Mocs</td><td>8</td><td>3.67</td><td>0.02</td><td>3.33</td><td>0.04</td><td>4.87</td><td>0.04</td></tr><tr><td>Knyahinya</td><td>5</td><td>3.57</td><td>0.11</td><td>3.53</td><td>0.10</td><td>4.82</td><td>0.30</td></tr><tr><td>"Corrected"</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Pultusk</td><td>9</td><td>3.79</td><td>0.03</td><td>3.61</td><td>0.16</td><td>5.35</td><td>0.07</td></tr><tr><td>Holbrook</td><td>20</td><td>3.67</td><td>0.04</td><td>3.41</td><td>0.09</td><td>4.69</td><td>0.05</td></tr><tr><td>L'Aigle</td><td>3</td><td>3.69</td><td>0.02</td><td>3.38</td><td>0.03</td><td>4.95</td><td>0.01</td></tr><tr><td>Mocs</td><td>8</td><td>3.67</td><td>0.02</td><td>3.33</td><td>0.04</td><td>4.87</td><td>0.04</td></tr><tr><td>Knyahinya</td><td>4</td><td>3.52</td><td>0.02</td><td>3.50</td><td>0.10</td><td>4.69</td><td>0.08</td></tr></tbody></table>

<figure><img src="image_9.png" /><figcaption>Fig. 6. In our limited set of data for non-ordinary chondrite meteorites, most meteorites appear to plot sufficiently far from the ordinary chondrites that a combined magnetic susceptibility and grain density measurement can discriminate among the different types. However, we note that Vigarano (CV) and Renazzo (CR) plot among the ordinary chondrite meteorites, and the scatter among aubrites is not easily explained. More data is needed to see how well this method can separate and classify various non-ordinary chondrite classes.</figcaption></figure>
chondrite meteorites known in 1803 were Ensisheim and Siena, both LL class, and Wold Cottage, an L. The most likely possibilities are either that the tag, or at least the mass written on the tag, is not contemporary with the fall; or it was erroneously connected with this sample before being sold by the Swiss meteorite dealer. Another possibility is that it happened to be a field meteorite collected at the same time as the L'Aigle fall and not recognized as a distinct fall until now.

In summary, we note that while seven of the 50 samples are discordant, three of those discrepancies can be explained as the result of weathering. However, we suggest that four of the samples may be mislabeled samples of different, unidentified meteorites. The chemical analysis of these particular samples to confirm this suggestion remains to be done. This rate of mismatch, if confirmed by the chemical analysis, is consistent with the previous result (Rochette et al. 2003) that at least 5% of the meteorites surveyed in a number of different collections are mislabeled, misclassified, or otherwise misidentified.

It is instructive to compare the range of densities and susceptibilities seen in these showers with those of the general classes of H, L, and LL meteorites shown in Fig. 1. Table 2 compares the range of these showers with and without the discordant samples.

If we eliminate those samples that are discordant, we find that in every case the clustering of samples, as measured by the standard deviation of their averages of grain densities and magnetic susceptibilities, is generally at least a factor of two tighter within a shower than for the class as a whole to which they belong. By contrast, the range of bulk densities is usually not significantly tighter within a shower compared to its class.

## COMPARISON WITH NON-ORDINARY CHONDRITES

The discussion here has concentrated on ordinary chondrites. They are by far the most common sort of meteorites and the differentiation between the classes of ordinary chondrites is one of the more common challenges facing meteorite collectors and curators. Because they are the most common, they also represent the bulk of the samples we have measured.

However, it is also worth determining if the combined grain density and magnetic susceptibility measures can distinguish between ordinary chondrites and other meteorite types. This would be especially useful for the discrimination of fusion-crusted, whole stone samples that in some cases can superficially look like ordinary chondrites. In our data set, we have only a few samples with simultaneous magnetic susceptibility and grain density measurements, but the relation between these values and the ordinary chondrites can be most illustrative.

As can be seen in Fig. 6, most achondrite meteorites have significantly lower magnetic susceptibilities than the ordinary

chondrites; this is not surprising, given that the classes measured here are essentially free of metallic nickel-iron. For the same reason, Rochette et al. (2002) report that most terrestrial rocks have magnetic susceptibilities that are significantly lower than ordinary chondrites. We lack data for any enstatite chondrites in our data set; however, Rochette et al. (2002) reported that the magnetic susceptibilities of other enstatite chondrites were higher than those of the H chondrites, and so again this system can discriminate them from any ordinary chondrite class (In fact, the magnetic susceptibilities of our enstatite chondrite samples were too high to be measured by the equipment used in 2001, when these measurements were taken.).

Carbonaceous chondrites present a different problem, however. In our data set, the CO and CV chondrites appear to have magnetic susceptibilities similar to those of the LL chondrites. The CO meteorites measured here have significantly higher grain densities, which allows them to be discriminated from the other classes, as does one CV (Allende); but the other CV shown here (Vigarano) plots in among the LLs. Likewise, the one CR sample (Renazzo) sits among the L chondrites in this plot.

Note that, unlike all the other data reported here, the Allende density is taken from earlier work (Consolmagno et al. 1998) and the Vigarano point represents the density of one sample but the magnetic susceptibility of a different piece of this meteorite.

Clearly, many more C type meteorites need to be measured before a strong conclusion can be made. However, it is important to note that in at least the limited data in hand at present, grain density and magnetic susceptibility alone may not discriminate between ordinary chondrites and some kinds of carbonaceous meteorites.

## CONCLUSIONS

The utility of magnetic susceptibility alone as a way of classifying ordinary chondrite falls was previously demonstrated by Rochette et al. (2003), and that scheme is confirmed by the data presented here. In every case where a sample's magnetic susceptibility falls outside the expected range for its type, we find that the grain density of that sample is also discordant in exactly the same way as to suggest that the sample is either heavily weathered or misclassified. Furthermore, the use of grain density along with magnetic susceptibility resolves the small overlap seen in the Rochette data between the magnetic susceptibilities of H and L chondrite falls. By contrast with grain densities, bulk densities of the meteorite do not provide a useful discriminant among H, L, and LL falls.

Finds and other heavily weathered meteorites are not as easily classified by susceptibility or density. However, finds and other heavily weathered samples will, by the nature of the weathering process, have essentially no porosity as the weathering of metallic iron in the meteorite fills the pore
space with iron oxides. Thus, although bulk densities themselves cannot help discriminate among different meteorite classes, the combination of bulk and grain densities permits the calculation of the meteorite's porosity which can then be taken as an indication of its weathering state. Furthermore, in our experience, such heavy weathering is almost always easily visible in the color and texture of the hand sample.

The core interest of this work is to provide a fast, non-destructive, and reliable means for classifying a meteorite or collection of meteorites. Before proceeding, one should confirm by inspection that the sample is most likely an ordinary chondrite and not heavily weathered. If that appears to be the case, then we conclude that the following steps can serve as a reliable way of classifying the sample as an H, L, or LL chondrite:

1. The first and most useful measurement to determine classification is the magnetic susceptibility. In many cases, this alone will be sufficient to determine the appropriate classification.

2. Measuring the grain density of the sample is very useful to resolve possible ambiguities and, in any event, to confirm the susceptibility classification.

3. Measuring the bulk density and using it to calculate a meteorite porosity is a useful final step in the classification process, as it allows a check on the weathering state of the sample and helps to discriminate between misclassification and weathering as the explanation for samples whose susceptibility and grain densities lie outside the expected range of a given meteorite.

Traditionally, meteorites are classified by their chemical properties. We have shown here that certain fundamental physical properties—magnetic susceptibility, grain density, and porosity—can also be useful discriminators of meteorite class and terrestrial history. Furthermore, such a measurement also provides a classification based on the properties of the whole rock and not just the chemistry of the small bit removed for analysis. And measuring these physical properties has the advantage of providing a simple, quick, nondestructive, and inexpensive method of surveying a large number of samples.

*Editorial Handling*—Dr. Timothy Swindle

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