Northwest Africa 5402

Algeria

Find: December 2005

Ordinary chondrite (LL6, porous impact melt)

History: Purchased by Greg Hupé in June 2008 from a Moroccan dealer in Rissani.

Physical characteristics: A single 189 g light gray stone with prominent small cavities exhibiting internal planar crystal faces

Petrography: (A. Irving and S. Kuehner, UWS): Grain size 0.1 to 0.4 mm, with an overall igneous texture. Prismatic grains of olivine and zoned low-Ca pyroxene are surrounded by interstitial or intercumulus plagioclase (or plagioclase glass), with accessory chromite, taenite, and troilite. Rare relict chondrules are observed. Areas with plagioclase compositions commonly exhibit triangular shapes in two dimensions, and have marginal inclusions of skeletal pyroxene (which appear to have grown from interstitial melt before plagioclase crystallized). Cavities are present within the interior of specimen as well as on the exterior, and do not appear to be plucked feldspar or other minerals, as their walls consist of euhedral to subhedral crystal faces of surrounding olivine and pyroxene grains without adhering plagioclase (Fig. 1).

Geochemistry: Olivine (Fa_28.8–30.5, FeO⁄MnO = 54.3– 63.3), low-Ca pyroxene (Fs_24.8Wo_4.0, FeO⁄MnO = 36.7), pigeonite (Fs_23.7–24.5Wo_7.9–9.7, FeO⁄MnO = 32.3–33.6), plagioclase (An_9.1–13.9Or_3.1–1.8).

Classification: Ordinary chondrite (LL6, S5, W1). This specimen appears to be the product of almost complete melting of an LL chondrite precursor followed by crystallization, but is unusual because of the preservation of apparently primary cavities (Fig. 2).

Specimens: A total of 20.3 g of sample and one polished thin section are on deposit at UWS. GHupé holds the main mass.

Fig. 1. False-colored BSE image of NWA 5402 showing its
texture and voids. Ol = olivine; Px = pyroxene; plag =
plagioclase; chr = chromite; troil = troilite.

Fig. 2. Cut surface of NWA 5717 (7.0 x 6.6 cm). Dark areas
are lithology A, light areas are lithology B.