Średni ciężar atomowy chondrytu Vicência (LL3.2)

Mean atomic weight Amean of Vicência (LL3.2 S1W0, fall 2013) ordinary chondrite has been calculated using literature data (Keil et al. 2015) on chemical composition of the meteorite and using relationships: between mean atomic weight and Fe/Si atomic ratio, between Amean and grain density, and between Amean and magnetic susceptibility. It was shown that Vicência’s Amean = 22.91 for composition without water. This value is close to the mean atomic weight of LL chondrite falls, is close to Amean value of LL3 chondrite falls, and is close to Amean value of Semarkona LL3.0 chondrite. Vicência’s Fe/Si atomic ratio (0.492±0.050) leads to Amean = 23.06–23.26, which is close to the value determined by bulk composition. Vicência’s Fe/Si atomic ratio is close to the value for Semarkona’s (Fe/Si = 0.511), and is close to LL’s mean Fe/Si ratio (0.520). This confirms that Vicência belongs to LL chondrites, as previously classified. Using dependence between mean atomic weight and grain density leads to Amean = 21.89±0.54 (dgr = 3.28 g/cm3, Keil et al. 2015), and using dependence between Amean and magnetic susceptibility gives Amean = 23.01±0.24 (logc = 4.30, Keil et al. 2015). Arithmetic mean of Amean (dgr), Amean (logc), and Amean(Fe/Si), gives 22.72±0.73, the value close to Amean(bulk composition) determined using compositional data. Mean atomic number Zmean, and Amean/Zmean ratio of the meteorite have been also calculated. Vicência’s Zmean = 11.37, and Amean/Zmean ratio is: 2.015 for composition without water. Vicência’s silicates shown the values: Amean = 21,67, Zmean = 10.76, Amean/Z mean = 2.014, Fe/Si = 0.318, Amean(Fe/Si) = 22.07–22.18, and Fe, Ni metal values: Amean = 56.63, Zmean = 26.53, and Amean/Z mean = 2.135. Two dependences: i) grain density dgr on Amean, and ii) grain density dgr on Fe/Si atomic ratio, were used to determine/verify grain density of Vicência chondrite. It was established that dgr(Amean) leads to the values: 3,42 g/cm3 for Vicência chondrite, 3,25 g/cm3 for silicates, and 7,90 g/cm3 for Fe, Ni metal of Vicência meteorite. Dependence dgr(Fe/Si) predicts density for Vicência chondrite: 3,47–3,49 g/cm3, and for silicates: 3,32–3,35 g/cm3.