Northwest Africa 13858 (NWA 13858)

Algeria

Purchased: 2020

Classification: Mesosiderite

History: (C. Muñecas, Expometeoritos) Sample was found by a nomad in Algeria (coordinates unknown). This meteorite was eventually purchased by Carlos Muñecas (Expometeoritos) from a dealer in Tindouf in 2020.

Physical characteristics: The sample is dark brown and is irregularly shaped with metal grains protruding through the exterior. The interior is a breccia of metal grains and silicates.

Petrography: Description and classification (A. Love, App) Sample is recrystallized breccia composed of (vol%): rounded-irregular-shaped masses of FeNi metal (25) and anhedral silicates (75) which show sutured grain boundaries and avg. grainsize of 516 µm (n=82). Pyroxenes and plagioclase both show poikiloblastic textures and olivine (2 vol%) contain well-developed reaction coronas. Additional minerals are: inverted pigeonite, high Ca pyroxene exsolution lamellae, merrillite, ilmenite, chromite, and both equant and lath shaped silica polymorphs.

Geochemistry: Olivine (Fa_28.2±5.5, Fe/Mn=39.4±2.2, n=4); low Ca pyroxene (Fs_30.1±4.1Wo_3.6±1.2, Fe/Mn=26.3±2.4, n=21); pigeonite (Fs_32.3±1.0Wo_6.3±1.3, Fe/Mn=26.9±0.9, n=7); high Ca pyroxene (Fs_17.2±1.5Wo_39.1±1.7, Fe/Mn=20.7±1.2, n=6); plagioclase (An_92.4±1.1Or_0.3±0.1, n=6).

Classification: Mesosiderite (estimated class A3). Mesosiderite based on abundance of metal and textures of silicates. Class A based on modal abundance of silicates (28 vol% plagioclase, 64 vol% Opx). Metamorphic type 3 based on recrystallized texture with sutured grain boundaries, absence of fine-grained regions, rare pigeonite and well-developed reaction coronas around olivine.

Specimens: C. Muñecas (Expometeoritos) holds the 1007 g main mass. A polished mount, an endcut and several small fragments weighing 24.32g are on deposit at App.