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Nowy chondryt zwyczajny L6, S1, W1: Northwest Africa 11779

100%

Przylibski T. A., Łuszczek K., Kryza R.

Acta Societatis Metheoriticae Polonorum

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2019

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vol. 10

121-139

EN

Based on petrological, mineralogical and geochemical research authors classified new meteorite Northwest Africa 11779 as the ordinary chondrite L6, S1, W1. Chemical composition of olivine crystals (Fa 24.9 mol.%) and of pyroxene crystals (Fs 19.4 mol.%) proved that this meteorite belongs to L chondrites. However, bulk chemical composition of NWA 11779 is not typical for L chondrites. Nevertheless, all analyzed elements (except Mo, Sn and Nb) are in abundances reported for L chondrites, some of elements have concentration closed to average abundances for L chondrites. The content of chosen, characteristic lithophile, siderophile and chalkophile elements in NWA 11779 chondrite is in most cases in accord with its typical abundance in L chondrites. Presence of poorly defined chondrules, secondary feldspar crystals larger than 50 µm in size, absence of glass within chondrules, coarse recrystallized matrix (with olivine crystals of 0.5 mm in diameter and pyroxene crystals of 0.3 mm in diameter) as well as carbon content below 0.2 wt% proved that studied meteorite belongs to the petrologic type 6. The only difference from characteristic features of petrologic type 6 in case of NWA 11779 chondrite is presence of ca. 10% of monoclinic Ca-poor pyroxenes. Undulatory extinction by olivine and absence of other shock features in this chondrite allow to determine the shock level as S1. Weathering grade of NWA 11779 was identified as W1 based on weathering of only FeNi alloy grains. The outer part of metallic grains as well as contact zones of FeNi and FeS are changed due to weathering. Between 10 and 20% of FeNi alloy grains are oxidized to iron oxides and hydroxides. These secondary products of weathering replace outer zone of FeNi grains and fill the small cracks, creating a few thin veins.

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Nowy chondryt zwyczajny H5, S2, W1: Northwest Africa 11778

100%

Przylibski T., Łuszczek K., Kryza R., Blutstein K.

Acta Societatis Metheoriticae Polonorum

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2020

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vol. 11

77-97

EN

Based on petrological, mineralogical and geochemical analyses, the authors classified the new meteorite Northwest Africa 11778 as an ordinary chondrite H5, S2, W1. It is a single stone with mass 767.5 g and with well-preserved black fusion crust with brown shade (Fig. 1). This meteorite was found in Sahara Desert and it was purchased by Wroclaw University of Science and Technology, Faculty of Geoengineering, Mining and Geology from Moroccan dealer in Zagora in June 2013. The most characteristic component of analyzed chondrite are different types of chondrules (barred olivine – BO, porphyritic olivine – PO, granular olivine – GO, radial pyroxene – RP, porphyritic olivine-pyroxene – POP, cryptocrystalline – C) (Fig. 2), which constitute 75% of meteorite. Their size is in range 0.2–1.2 mm, with average chondrule size ca. 0.6 mm. Bigger porphyritic olivine chondrules with diameter up to 1.5 mm rarely occur. The chemical composition of olivine crystals (Fa 18 mol%) and pyroxene crystals (Fs 16.2 mol%) proves this meteorite to be an H chondrite (Tab. 1, Fig. 4–5, App. 1–2). The averaged concentration of major elements in the classified meteorite is comparable to their mean content in H chondrites (Fig. 8). The meteorite NWA 11778 contains only slightly less Mg and Al than average H chondrites (Tab. 2). Among the other analysed elements, values distinctly out of the range of typical concentrations for H chondrites are characteristic of Hg and Eu (lower concentration in the NWA 11778 meteorite) (Tab. 3, Fig. 8–9). The presence of chondrules with predominantly sharp boundaries (Fig. 2), secondary feldspar crystals with sizes of up to 50 mm, chiefly crystalline mesostasis and only secondarily – devitrified glass in chondrules, and transparent crystalline matrix (with olivine crystals up to 0.26 mm and pyroxenes up to 0.30 mm in size), as well as common occurrence of untwinned rhombic pyroxenes prove the classified meteorite to belong to petrological type 5. It is additionally confirmed by mean Ni content in troilite below 0.5 wt% (0.04 wt%) (Tab. 1, App. 4) and carbon content below 0.2 wt% (0.07 wt%) (Tab. 2). Undulatory extinction in some olivine and pyroxene crystals and the presence of irregular fractures in the NWA 11778 chondrite enables specifying its shock level as S2. The weathering grade adopted for the NWA 11778 chondrite was W1, as visible weathering changes cover only the marginal parts of FeNi alloy grains. As a result of the weathering of 10–20% of FeNi grains, iron oxides and hydroxides are formed. These secondary weathering Fe3+ compounds also fill cracks, forming veins running between chondrules within matrix (Fig. 3).

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Chondryt Sołtmany

51%

Przylibski T. A.

Acta Societatis Metheoriticae Polonorum

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2016

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vol. 7

93-122

EN

The Sołtmany hammer meteorite is classified as an ordinary chondrite type L6, W0, S2. At present it is the most thoroughly and comprehensively examined Polish meteorite. A comprehensive petrological, mineralogical and geochemical analysis alongside the investigation of its physical and particularly thermophysical properties, and, most of all, analyses of cosmogenic radionuclides and noble gases isotopes content, as well as the use of a troilite thermometer has made it possible to draw interesting conclusions concerning the genesis and evolution of the parent body and the history of the parent meteoroid and, finally, the Sołtmany meteorite. The present report attempts at summing up the results of studies conducted at several European research centres in the last four years. The age of the the Sołtmany chondrite parent rock has been defined at 4.137 billion years. It was formed at a temperature of up to 440–450 K (about 170°C), probably at a depth of up to 3 to 7 km under the surface of the parent body, i.e. at a pressure of the order of 1–2.4 kbar. Such a low temperature during the accretion, diagenesis and metamorphism of the parent body may point to its complicated development, which may be in part due to collisions of partially melted planetesimals. Like with other type L ordinary chondrites, one can infer that the parent body could have been destroyed about 467 million years ago, at the time of a catastrophic collision which led to the formation of Gefion family of planetoids. Perhaps one of the bodies in this family was involved in another collision about 29.2 million years ago, which resulted in ejecting the parent meteoroid of the Sołtmany chondrite onto the Earth collision trajectory. Before entering the Earth’s atmosphere, this meteoroid had the mass of about 36 kg and the diameter of ca 13.5 cm. During its flight through the atmosphere, it rotated and somersaulted, which resulted in the formation of an uniform thin (0.5–0.7 mm) fusion crust, whose temperature reached 1000°C. In the last phase, the Sołtmany meteorite fell almost vertically and its mass was a mere 3% of the mass of the parent meteoroid – 1.066 kg. It hit the roof and then the concrete stairs of a farm building, which caused it to break into two bigger and many small pieces. It was found a few minutes after the fall, which occurred at 6:03 a.m. (CEST, UTC+2:00) on 30 April 2011, by Wydmińskie Lake in northern Poland (54°00,53’N, 22°00,30’E). The Sołtmany chondrite is one of just 14 meteorites in which the activity concentration of the cosmogenic 52Mn has been determined, and one of the few ordinary chondrites where the concentration of organic matter has been defined. As a result, it was found out that unlike in carbonaceous CI chondrites, the composition of organic particles is dominated by less complex compounds (CHO and CHOS) than CHNO and CHNOS compounds. This may indicate the decomposition of more complex organic compounds into particles with simple structures during magmatic and metamorphic processes related to formation of type L ordinary chondrites.

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Nowy chondryt zwyczajny L6, S1, W1: Northwest Africa 11779

Nowy chondryt zwyczajny H5, S2, W1: Northwest Africa 11778

Chondryt Sołtmany