Northwest Africa 13919 (NWA 13919)

Algeria

Find: 2019

Classification: Ordinary chondrite (LL3)

History: The meteorite was found by nomads in Algeria in 2019. Zs. Kereszty purchased the stone from a Moroccan dealer from the city of Guelmim in October 2020.

Physical characteristics: (D. Rezes and Zs. Kereszty, CSFK) Originally an individual egg-shaped (3 × 4 × 4.5 cm) brown stone (74.1 g) without fusion crust. The stone has shiny, dark desert varnish on most of its sides. On the surface of the stone many different colored (green, bluish gray, black) chondrules bulge out from the brown groundmass. Largest objects on the surface are a chondrule with 0.8 mm diameter and a black clast with 0.9 mm length. Cut surface reveals scarce shiny metal and sulfide phases. Inside the stone there are two distinct lithologies with intact, well-defined chondrules (radial, barred, granular, porphyritic and bleached textures). One of the two lithologies shows densely packed chondrules with rare matrix material. This part contains a black clast. The other one shows loosely packed chondrules with more abundant matrix. The boundary of the two parts is not sharp.

Petrography: (D. Rezes, CSFK) Chondrite composed of well-defined chondrules with average diameter of 840 µm, N=94 (Lithology 1) and 804 µm, N=32 (Lithology 2). Largest chondrule of the thin section has 4582 µm length and 3144 µm width. Minor mineral phases are FeNi, troilite and Fe,Ni-sulfides. Lithology 1 shows densely packed chondrules with rare opaque matrix material, while Lithology 2 shows loosely packed chondrules with more abundant matrix that contains broken chondrules and crystals. Devitrified mesostasis is present in several chondrules, however chondrule glass is still observable in both lithologies.

Geochemistry: (D. Rezes, CSFK) Lithology 1 (densely packed chondrules, rare matrix material): Chondrule ferroan olivine Fa_26.2±8.4 (range Fa_10.3-41.9), CaO(wt%)=0.12±0.06 (range 0.03-0.31), Cr₂O₃(wt%)=0.06±0.06 (range 0.00-0.31), Fe/Mn=63.1±16.1, N=61; enstatite Fs_2.8±0.1Wo_0.6±0.1 (range Fs_2.7-2.8Wo_0.4-0.8), Fe/Mn=17.2±5.2, N=4; augite crystallites Fs_18.9±5.1Wo_38.4±3.5 (range Fs_14.0-23.4Wo_34.9-41.7), Fe/Mn=18.8±10.5, N=4; Glass in type-II chondrules SiO₂=65.25±2.25, TiO₂=0.49±0.13, Al₂O₃=12.02±2.01, Cr₂O₃=0.20±0.25, FeO=5.54±1.89, MnO=0.10±0.04, NiO=0.01±0.01, MgO=6.14±2.70, CaO=1.95±0.91, Na₂O=7.82±1.28, P₂O₅=0.38±0.30, SO3=0.09±0.26, N=8 (all in wt%); Matrix S(wt%)=0.29±0.10, N=4. Lithology 2 (loosely packed chondrules, more abundant matrix): Chondrule ferroan olivine Fa_27.0±9.9 (range Fa_6.7-40.7), CaO(wt%)=0.16±0.09 (range 0.01-0.43), Cr₂O₃(wt%)=0.07±0.06 (range 0.00-0.27), Fe/Mn=69.4±18.4, N=46; enstatite Fs_15.5±7.2Wo_1.8±1.6 (range Fs_7.6-23.2Wo_0.2-4.2), Fe/Mn=23.2±2.2, N=12; pigeonite Fs_22.6±0.5Wo_8.5±1.8 (range Fs_22.2-23.3Wo_6.9-10.9), Fe/Mn=25.3±1.1, N=4; Glass in type-II chondrules SiO₂=66.74±4.71, TiO₂=0.54±0.10, Al₂O₃=14.02±1.38, Cr₂O₃=0.18±0.22, FeO=3.26±0.65, MnO=0.08±0.05, NiO=0.01±0.02, MgO=2.45±1.24, CaO=3.19±2.49, Na₂O=8.05±0.96, P₂O₅=1.23±0.51, SO3=0.26±0.42, N=7 (all in wt%); Matrix S(wt%)=0.34±0.14, N=4.

Classification: Brecciated unequilibrated ordinary chondrite (LL3), estimated subtypes of the lithologies are LL3.3 and LL3.4. LL based on average chondrule diameter and low metal content. Subtype is based on mean Cr₂O₃-content and sigma of ferroan olivine from Grossman and Brearley (2005). The Cr₂O₃ values and standard deviation of ferroan chondrule olivines are in the field of UOCs with petrologic type >3.2. The presence of glass in chondrules indicate petrologic type <3.5. Shock stage S2, weathering grade W2.

Specimens: 15 g on deposit at CSFK, ZKereszty holds the main mass.