Northwest Africa 13688 (NWA 13688)

(Northwest Africa)

Find: 2016

Classification: Ordinary chondrite (L6)

History: The specimen was bought from Zs. Kereszty in 2017.

Physical characteristics: Originally an individual pyramidal-shaped (5 × 5 × 4 cm) brown stone (129.2 g) without fusion crust. Cut surface reveals grey lithology with several limonitic patches around troilite, metal and opaque veins.

Petrography: (D. Rezes, CSFK) Almost all of the metal and troilite phases are affected by oxidation, without the alteration of silicate phases. Approximately half of the silicates are stained by limonitic patches. There are just three thin (50 µm) shock veins in the section. Mosaicism of olivine grains and several chromite-plagioclase assemblages are observed in the sample. Both sparse relict chondrules and polygonal crystals with triple junctions are presented. Plagioclase crystals have interconnected network up to 1 mm.

Geochemistry: (D. Rezes, CSFK) Olivine Fa_25.4±0.2, Fe/Mn=51±9, N=10; orthopyroxene Fs_22.1±0.4Wo_1.9±0.2, Fe/Mn=30±2, N=9; plagioclase Or_7.9±1.8Ab_79.6±3.1An_12.5±1.6, N=12; CaO-content in orthopyroxenes 1.0±0.1 wt% (0.8-1.2 wt%; N=9)

Classification: Ordinary chondrite (L6), shock stage S4, weathering grade W3. CaO-content of orthopyroxenes and the presence of several relict chondrules along with equilibrated polygonal crystals with triple junctions indicate a highly recrystallized type 6 chondrite.

Specimens: 58.5 g on deposit at CSFK, D. Rezes holds the main mass including one polished thin section.