Modern systems of classification has been started in XIX century. However the true progress was began at 60’s and 70’s of XX century. In this time was started modern analythic methods such as: chemical, mineralogic and pretrographic analysis. For this progress fostered also a large number of found meteorites from Antarctica. This article will be concerned about a classification of ordinary chondrites. Acquired meteorite from moroccan searchers. Has been examined and classified. The scheme of this works are presented below.
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Współczesny system klasyfikacji meteorytów pochodzi z końca XIX w. Prawdziwy rozwój nastąpił dopiero w latach 60 i 70 XX, kiedy pojawiły się nowoczesne metody badawcze, umożliwiające bardziej kompleksowe analizy petrologiczne, zwłaszcza chemiczne. Rozwojowi temu też sprzyjała olbrzymia ilość meteorytów znajdowanych na Antarktydzie. Niniejsza praca przybliży czytelnikowi sposób klasyfikacji meteorytów kamiennych typu chondryty. Materiał jako przykład badawczy posłużył meteoryt kamienny zakupiony w 2012 w Maroku.
NWA 4967 carbonaceous chondrite thin section was investigated by optical microscopes in transmission and in reflection. Minerals of the meteorite have been identified and microstructure analyzed. Chondrules, matrix, metal phases, AOAs and CAIs are constituents of the rock, as expected. Olivine, clinopyroxene, orthopyroxene, troilite, kamacite and feldspar have been detected. Various types of chondrules including: PO, POP, PP, RP, BO, C, GOP and GO chondrules were identified. Compositional zoning of some olivines, diagnostic cracks in pyroxenes, clinopyroxene twins, and chondrule rims have been observed and analyzed. Our previous EPMA and Raman data as well as present optical data confirm that NWA 4967 belongs to CO3.2 chondrites, as previously classified.
Mean atomic weight Amean of Sołtmany (L6, S2, W0) ordinary chondrite, various L6 chondrites such as: Jesenice, Girgenti, Leedey, Bruderheim, Holbrook and Modoc, as well as LL, L and H chondrites has been determined using literature data on chemical composition of the meteorites. Relationship between mean atomic weight and Fe/Si atomic ratio for ordinary chondrites has been established. It was shown that Sołtmany’s Amean = 23.97 is close to mean atomic weight of L chondrites Amean = 23.70, and is close to mean atomic weight of L6 chondrites Amean = 24.06±0.16. It has been established that Sołtmany’s Fe/Si atomic ratio (Fe/Si = 0.588) is close to Fe/Si ratio for L6 chondrites (Fe/Si = 0.598). This means that Sołtmany belongs to L6 chondrites, as previously classified. Using discovered by the author (Szurgot, 2015) dependence between mean atomic weight and uncompressed density of planetary matter it was established that grain density of Sołtmany meteorite should be equal to 3.56±0.12 g/cm3, which is about 4% lower than previously estimated by porosity data. Mean atomic weight of extraterrestrial minerals present in ordinary chondrites and in Sołtmany meteorite have been also determined.
Mean atomic weights Amean of Siena (LL5, fall 1794), Hautes Fagnes (LL5, S1, W1, find 1965) and NWA 7915 (LL5, S2, W3, find 2010) ordinary chondrites have been determined using literature data on chemical composition of the meteorites and using relationship between mean atomic weight and Fe/Si atomic ratio (Szurgot 2015). It was shown that NWA 7915 Amean = 22.80 is close to mean atomic weight of LL chondrites (Amean = 23.00), and is close to mean atomic weight of LL chondrite falls (Amean = 22.90, Szurgot 2015). NWA 7915’s Fe/Si atomic ratio (0.529) leads to Amean = 23.28 which is close to the value determined by bulk composition. This means that NWA 7915 belongs to LL5 chondrites, as previously classified (Brawata et al. 2014). Mean atomic weight Amean of Hautes Fagnes determined by bulk composition is between 23.11 and 23.35. Lower Amean value is close to Amean of LL chondrites, but higher value is the same as Amean of intermediate L/LL chondrites (23.34 for L/LL, Szurgot 2016). Hautes Fagnes Fe/Si atomic ratio and Amean(Fe/Si) are identical with those for NWA 7915 (Fe/Si = 0.529, Amean = 23.28). Amean data indicate that Hautes Fagnes can belong to LL5 chondrites, as previously classified (Vandeginste et al. 2012) or can be one of L/LL chondrites. Mean atomic weight of Siena meteorite is much higher than expected for LL chondrite. Siena’s bulk composition gives Amean = 24.47, and Amean(Fe/Si) dependence gives Amean = 24.45 (Fe/Si = 0.7345). Using dependence between mean atomic weight and grain density (Szurgot 2015) leads to Amean = 23.24 (dgr = 3.46 g/cm3, Macke 2010), and using dependence between Amean and magnetic susceptibility (Szurgot 2016) gives Amean = 23.53±0.13 (logc = 4.65±0.09, Macke 2010). Bulk composition and Fe/Si ratio indicate that Siena has the same Amean as intermediate H/L chondrites, for which Amean = 24.3 (Szurgot 2016). Grain density indicates rather L/LL intermediate group for Siena, and magnetic susceptibility indicates intermediate L/LL or L chondrites (23.34 for L/LL, and 23.67 for L, Szurgot 2016). Mean atomic number Zmean, and Amean/Zmean ratio of the three meteorites have been also determined. Siena’s Zmean = 12.104, Hautes Fagnes Zmean = 11.445–11.562, and NWA 7915’s Zmean = 11.293. Amean/Zmean ratios are: 2.022 for Siena, 2.019–2.020 for Hautes Fagnes, and 2.019 for NWA 7915.
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