Northwest Africa 13685 (NWA 13685)

Mauritania

Purchased: 2020

Classification: Rumuruti chondrite (R3-6)

History: Two samples weighing a total of 486 g were found prior to 2020. Carlos Muñecas purchased the samples from a dealer in Mauritania in 2020.

Physical characteristics: Samples are irregularly shaped and have a wind-ablated dark brown exterior. A cut face shows the interior is composed of abundant chondrules and sulfides.

Petrography: Description and classification (A. Love, App) Sample is a genomict breccia composed of unequilibrated lithic clasts set within a host of unequilibrated chondrules and fragments in a slightly recrystallized matrix. Sample contains a large amoeboid shaped clast composed of olivine and clinopyroxene and connected networks of secondary plagioclase (avg grainsize 50 µm, n=96). Average chondrule diameter is 353 µm, n=72. Sample contains rare CAIs. Additional minerals are: pentlandite, troilite, chromite, rare orthoclase, plagioclase and apatite.

Geochemistry: Host: Olivine (Fa_29.0±15.5 (Fa_4.2-44.7), CV%=53 (type 3 material) Fe/Mn=70.8±31.1, n=25); low Ca pyroxene (Fs_11.7±7.8Wo_1.4±1.5, Fe/Mn=26.6±24.5, n=11); pigeonite (Fs_32.0Wo_8.9, n=1); high Ca pyroxene (Fs_10.3±7.8Wo_38.4±2.0, Fe/Mn=31.0±19.4, n=4); equilibrated clast: (Fa_37.8±0.3, Fe/Mn=75.5±1.7, n=7); pigeonite (Fs_31.2±0.2Wo_7.1±0.2, Fe/Mn=43.2±1.2, n=3); high Ca pyroxene (Fs_16.9±0.9Wo_37.3±1.7, Fe/Mn=39.9±1.0, n=4).

Classification: Rumuruti chondrite (R3-6 breccia C-S3 wi-2). Chondrule diameter, magnetic susceptibility, ubiquitous pentlandite and lack of FeNi metal suggest sample is an R chondrite. Based on unequilibrated compositions of clast and host, sample is an R3.5. Equilibrated mafic silicate compositions, recrystallized texture and grainsize of secondary plagioclase suggests clast is a type-6 R chondrite.

Specimens: Carlos Muñecas holds the 269 g main mass. Several fragments and a sliced end piece weighing a total of 22.73 g and a polished thin section and mount are on deposit at App.