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THE NARAGH METEORITE: A NEW OLIVINE‐BRONZITE CHONDRITE FALL
Author(s) -
Adib D.,
Liou J.G.
Publication year - 1979
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1979.tb00502.x
Subject(s) - troilite , chondrule , olivine , meteorite , chondrite , chromite , plagioclase , geology , mineralogy , augite , geochemistry , analytical chemistry (journal) , chemistry , astrobiology , physics , quartz , paleontology , chromatography
At 9:20 A.M. on August 18, 1974, a stony meteorite of approximately 3200 grams struck the roof of a secondary school at Naragh, Central Iran, (51°30′E, 33°45′N). The ellipsoidal dark‐gray meteorite was 17 × 15 × 13 cm (density 3.62 gr/cm 3 ). XRF and wet chemical analysis yields the bulk composition of the meteorite as follows in weight percent: Fe 11.95, Ni 1.05, Co 0.07, FeS 5.49, SiO 2 37.15, TiO 2 0.15, Al 2 O 3 2.43, Cr 2 O 3 0.62, FeO 14.25, MnO 0.23, MgO 23.79, CaO 1.61, Na 2 O 0.92, K 2 O 0.08, P 2 O 5 0.26. Modal mineral contents (in volume percent) are olivine 40, orthopyroxene 25, clinopyroxene 3, plagioclase 10.5, chromite 0.80, phosphate 0.70, troilite 6, metal phases 14. The meteorite is fine‐grained, with average grain size about 0.4–0.6 mm and contains numerous recrystallized glassy chondrules. Olivine occurs as laths and radiating crystals in chondrules and as coarse‐grained phenocrysts and interstitial microcrystalline grains in the matrix. These olivines have relatively uniform composition (Fo 80–82 Fa 20–18 ). Fine‐grained skeletal orthopyroxenes of average composition (En 16 Fs 82 Wo 01 ) are inter‐grown with olivine in both chondrules and matrix. Clinopyroxene and plagioclase of average composition (En 6.5 Fs 48 Wo 45.5 ) and (Ab 82 An 12 Or 06 ) respectively, are evenly distributed in the matrix, together with kamacite (Fe 92–95 ), plessite (Fe 69.6–82.2 ) and taenite (Fe 46.7–66.1 ), troilite (Ni‐free) and chromite grains . The high ratios of total Fe to SiO 2 of 0.71, metallic Fe to total Fe of 0.54, and SiO 2 to MgO of 1.56 in the bulk composition, the Fa component of olivine grains of 17.5–19.6, and the high Ca content of orthopyroxenes between 0.53 and 0.87 wt % suggest that the Naragh meteorite belongs to the H‐group and petrologic type 6 of Van Schmus and Wood (1967) classification. In addition, the occurrence of fine‐grained clear sodic plagioclase, the presence of numerous recrystallized chondrules with homogeneous silicate minerals, and the absence of Ni in the sulfide phase indicate that the Naragh meteorite has been metamorphosed after the initial crystallization in the parental body .