2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

Characterization and classification of the first meteorite fall in Varre-Sai town, southeast Brazil, using X-ray microfluorescence technique

Haimon D.L. Alves¹, Joaquim T. de Assis², Claudio Valeriano³ and Caio Turbay4

1 Programa de Engenharia Nuclear, COPPE/UFRJ Cidade Universitária, Rio de Janeiro, RJ, Brazil [email protected]

2 Instituto Politécnico, UERJ Rua Alberto Rangel, s/n, Nova Friburgo, RJ, Brazil [email protected]

3 Departamento de Geologia, UERJ Rua São Francisco Xavier, 524, Rio de Janeiro, RJ, Brazil [email protected]

4 Departamento de Geologia, UFES Alto Universitário, s/n, Alegre, Espírito Santo, Brazil [email protected]

ABSTRACT

On the night of June 19th, 2010, a meteorite fell nearby the town of Varre-Sai, Rio de Janeiro state, southeast Brazil. A small part of it was found and taken for analysis. A meteorite analysis can give researchers a better understanding of the origins of the Universe. However, some of the most traditionalist methods of characterization and classification of meteorites are destructive. In this paper we present the results of a chemical analysis and classification of this particular meteorite using X-ray microfluorescence (µXRF), a non- destructive technique that allows for a quick and easy elemental analysis within the range of micrometers. Both sides of the meteorite were measured, 35 points in total, using Artax, a state of the art µXRF system developed by Bruker, at 50 kV tension and 700 µA current. Quantitative analysis using Direct Comparison of Counting Rates (DCCR) method showed concentrations of iron and nickel together of roughly 7.86%. We found that it is possible to distinguish this meteorite from most of the categories as an ordinary L-type chondrite but a more thorough analysis might be necessary so as to obtain a more detailed classification.

1. INTRODUCTION

A meteorite is defined as an object originating from outer space that reaches Earth’s ground before it disintegrates. Its origin can be from small astronomical objects or by the collision of asteroids. After passing through the Earth’s atmosphere, the resistance causes the meteorite to heat up and emit light then becoming known as a meteor. [1] Meteorites can be classified basically into three broad categories depending whether they are mainly composed of rocky material, metallic material or mixtures: a. Stony meteorites b. Iron meteorites c. Stony-iron meteorites

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

Modern classification divides meteorites also into groups according to structure, chemical and isotopic composition and mineralogy. [2]

1.1. Meteorite classification [3]

1.1.1. Stony meteorites The majority of meteorite falls are stony meteorites consisting mainly of silicate minerals. They are classified between chondrites and achondrites.

1.1.1.1. Chondrites Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They are named for the small, round particles prominent among the components present in chondrites. These are the chondrules, usually rich on iron and nickel components. About 86% of the meteorites that fall on Earth are chondrites. Chondrites can also be divided depending on iron and nickel concentrations, as follows: [4] a. H-type chondrite – High total iron and nickel of 15~20% b. L-type chondrite – Low total iron and nickel of 5~11% c. LL-type chondrite – Low total iron and contents of 2~5%

1.1.1.2. Achondrites Achondrites are stony meteorites that, as the name suggests, doesn’t contain chondrules. They have been differentiated and reprocessed due to melting or differentiation of the parent body. As a result, they have distinct textures and mineralogies that indicate igneous processes. About 8% of the meteorites that fall on Earth are achondrites.

1.1.2. Iron meteorites Iron meteorites have an elemental composition consisting largely of nickel-iron alloys. Although rare in comparison with stony meteorites, around 5% of witnessed falls, they are easily recognized, more resistant to weathering and are much more likely to be found in larger pieces, since they are more resistant to the impact with the Earth’s atmosphere. 90% of the mass of all known and registered meteorites are from iron meteorites.

1.1.3. Stony-iron meteorites

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

This type of meteorite is extremely rare representing only 1% of witnessed falls. They consist of a mixture of equal parts of nickel and iron and different types of stony components, such as silicates. They can be divided in pallasites and mesosiderites.

1.1.3.1. Pallasites Pallasites are described by a certain structural class of stony-iron meteorites that contains abundant silicate inclusions in a nickel-iron matrix where usually the silicates are large olivine crystals. Sometimes they are used in jewelry because of its gem quality.

1.1.3.2. Mesosiderites Mesosiderites are composed of approximately equal parts of metallic nickel-iron and silicate. Broken fragments of minerals cemented together makes for its irregular texture.

1.2. X-ray microfluorescence analysis The X-ray microfluorescence (µXRF) is a nondestructive elemental analytical technique that allows for easy and quick results related to the sample’s elemental composition in the range of precision of micrometers expanding the applications of common XRF to smaller areas and objects. Primary X-rays are produced in an X-ray tube by accelerating electrons towards a target, the material of the tube anode. When reaching the target, these high-energy electrons are decelerated and emit a continuous spectrum, called bremsstrahlung. Using this continuous spectrum into the sample, characteristic radiation related to each element can be obtained. Since each element has electronic orbitals of characteristic energy, they also emit characteristic secondary X-rays by means of photoelectric effect. This secondary radiation can be detected by a detector and associated electronic components. The results will then be seen into a computer relating counting of photons detected and energy of these photons. [5,6] The objective of this work is to classify this meteorite by means of the elemental composition obtained through X-ray microfluorescence. Since its size ranges around 2cm³ µXRF makes it possible to acquire enough data for good statistical analysis.

2. Experimental Setup

2.1. Artax 200 The µXRF system, Artax 200 (Figure 1), from Bruker, consists of an X-ray tube with Molybdenum target. Maximum parameters were used: 50 kV tension and 700 µA current; and a collimator of 650 µm. Alignment (Figure 2) was obtained through an inputted camera

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5 and a laser. 35 measurements were made, each 5 minutes long. Spectral analysis was made using Spectra software, from Bruker. Quantitative analysis was made through Direct Comparison of Counting Rates (DCCR) method using a certified alloy provided by Bruker.

Figure 1: Artax 200

Figure 2: Positioning of sample

2.2. Sample A meteorite (Figure 3) found in Varre-Sai town, southeast Brazil, was analyzed in this work. [7] No chemical or physical preparation were done.

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

Figure 3: Meteorite of Varre-Sai

3. Results and Discussion 35 measurements were made: 23 points on the white side and 12 points on the black side. Figure 4 and 5 shows one point measured from the white side of the meteorite and an XRF spectrum obtained from it, respectively. Figure 6 and 7 shows one point measured from the black side of the meteorite and an XRF spectrum obtained from it, respectively. Elemental analysis gave composition of Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu and Zn. Ar and Mo were also found but Ar is an element commonly found in air and Mo is characteristic from the tube anode. Concentrations of Nickel and Iron were calculated (Table 1) because they are the elements that can mainly differentiate the types of meteorites using an elemental analysis tool like µXRF.

Figure 4: White side of meteorite

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

x 1E3 Pulses

4.0

3.0

Mo K Ti Fe Cu Si Ar Ca Cr Mn Ni Zn Si Mo Ar K Ca Ti Cr Mn Fe Ni Cu Zn Mo

2.0

1.0

0.0 2 4 6 8 - keV - Figure 5: XRF spectrum of white side

Figure 6: Black side of meteorite

x 1E3 Pulses

3.0

Mo K Ti Fe Cu Si Ar Ca Cr Mn Ni Zn 2.0 Si Mo Ar K Ca Ti Cr Mn Fe Ni Cu Zn Mo

1.0

0.0 2 4 6 8 - keV - Figure 7: XRF spectrum of black side

INAC 2011, Belo Horizonte, MG, Brazil.

2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

Table 1: Concentrations of Nickel and Iron together and its standard deviation

Measurement Fe+Ni(%) () 1 6.93 0.009 2 7.27 0.012 3 6.08 0.01 4 7.23 0.01 5 5.97 0.008 6 6.28 0.01 7 5.53 0.008 8 8.44 0.011 9 6.11 0.009 10 5.88 0.009 11 8.42 0.012 12 6.30 0.009 13 8.60 0.011 14 6.95 0.008 15 7.47 0.011 16 6.65 0.01 17 5.91 0.009 18 7.62 0.014 19 7.63 0.012 20 7.26 0.009 21 8.26 0.011 22 6.15 0.01 23 10.50 0.012 24 6.69 0.012 25 6.74 0.011 26 8.79 0.012 27 6.94 0.011 28 16.40 0.018 29 9.65 0.014 30 13.86 0.016 31 6.97 0.012 32 6.97 0.012 33 6.97 0.012 34 12.87 0.016 35 8.80 0.013

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2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5

4. Conclusions The quantitative elemental analysis gave concentrations of iron and nickel together of roughly 7.86%. Since the major components of meteorites are iron and nickel, it is possible to try and classify it as a stony, iron or stony-iron meteorite using µXRF. Most of the measurements have concentrations between 5 and 10% with only four exceptions. These four measured points are found in the black side of the meteorite, the one that burned because of the air resistance as it entered the Earth’s atmosphere, and may be the reason why these points are not within the expected values of iron and nickel concentrations. As the meteorite burned, it is possible that some other elements were lost and concentrations of the remaining elements randomly rose. Since iron and nickel didn’t show concentrations of equal proportions, they can’t be classified as a stony-iron meteorite and since its values are not that high, they can’t be classified as an iron meteorite. Its classification should be then of a stony meteorite. Concentrations of nickel and iron together between 5 and 10% are usually classified within stony meteorites as an ordinary L-type chondrite. Although the results showed that it is possible to classify a meteorite as an ordinary L-type chondrite, its petrological type can’t be determined by means of elemental composition. In this case a more thorough analysis is necessary.

ACKNOWLEDGMENTS The authors would like to thank Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro for the financial support.

REFERENCES

1. D.W. Sears, “The Nature and Origin of Meteorites”, New York, Oxford University Press, (1978); 2. M. Terho, L. J. Pesonen, I. T. Kukkonen, M. Bukovanská. “The petrophysical classification of meteorites”, Studia Geophysica et geodaetica, 37, Number 1, pp. 65-82 (1993); 3. R. N. Clayton, N. Onuma, T. K. Mayeda, “A classification of meteorites based on oxygen isotopes”, Earth and Planetary Science Letters, 30, Issue 1, pp. 10-18 (1976); 4. W.R. Van Schmus, J.A. Wood, "A chemical-petrologic classification for the chondritic meteorites". Geochimica et Cosmochimica Acta, 31, Issue 5, pp. 747-765 (1976); 5. R. Schlotz, S. Uhlig, “Introduction to X-ray Fluorescence (XRF)”, Bruker AXS GmbH, Karlruhe, West Germany, (2006); 6. B. Beckhoff, B. Kanngießer, N. Langhoff, Wedell H.Wolff, “Handbook of Practical X- ray Fluorescence Analysis”, Springer-Verlag Berlin Heidelberg, (2006); 7. A. O. Chaves, C. Turbay, G. Sgarbi, A. Romano, L. Garcia, “O meteorito condrítico ordinário L5(S5) de queda em Guaçuí, ES-Brasil”, Revista Escola de Minas, 64, Número 1, (2011);

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