Northwest Africa 14261 (NWA 14261)

(Northwest Africa)

Purchased: March 2014

Classification: Ordinary chondrite (L3-5)

History: One of several Northwest African whole stones purchased via online by DChenin from an American collector named Bill Hall who owns a Rock and Gem shop in Bend, OR. The stone was cut into slices; six were sent to Cascadia.

Physical characteristics: Physical Characteristics: Cut faces are dark brownish gray with easily distinguished chondrules. Weathering is uneven, with replacement of metal along fractures. Metal is relatively abundant in some slices, including the one used for thin sectioning, while being mostly replaced in other slices. Slightly lighter-colored roughly equant clasts are visible in most slices; the largest is ~2 × 2 cm in area. Rare black clasts are visible in two of the six slices; the largest is ~2.5 × 1.3 mm in area.

Petrography: (M. Hutson, A. Ruzicka, Cascadia): The thin section contains a host lithology that encloses a clast similar to the host lithology, part of one of the lighter-colored clasts, and two small black clasts. The host lithology is composed of distinct chondrules and chondrule fragments set in a dark matrix; zoned olivine is abundant in BSE images. A small (~5 × 2.5 mm across) clast similar in appearance to the host lithology is distinguished by textural discontinuities at its border. Chondrules are integrated with matrix in the lighter-colored clast, which contains plagioclase feldspar grains ?40 microns across; mineral chemistry indicates that the clast is equilibrated. The black clasts are entirely opaque in transmitted light. In BSE imaging, the black clasts are composed of a couple of cryptocrystalline chondrules and numerous rounded grains and clasts set in a fine-grained igneous-textured matrix. The section contains abundant sulfide; it forms partial rims around chondrules in the host lithology. Both the host lithology and equilibrated clast contain merrillite; the black clast contains chlor-apatite. The black clast also contains a silica polymorph and a few small grains of an aluminous spinel.

Geochemistry: Olivine Fa_24.6±6.4, N=34 (host), Fa_25.1±12.8, N=20 (small clast similar to host), Fa_23.5±0.2, N=24 (equilibrated clast), Fa_10.8±8.5, N=22 (black clast); Low-Ca pyroxene: Fs_15.1±9.4Wo_1.2±0.9, N=16 (host), Fs_14.02±7.4Wo_1.3±1.0, N=7 (small clast similar to host), Fs_19.4±0.4Wo_1.4±0.2, N=16 (equilibrated clast), Fs_7.9±9.5Wo_3.2±1.2, N=15 (black clast). Black clast: single spinel grain: Mg# 87.3, Cr# 0.6.

Classification: Ordinary chondrite (L3-5) based on mineral chemistry and texture. The small clast similar to the host appears to be a low subtype 3 based on mineral chemistry.

Specimens: Cascadia holds 201.5 g in six pieces, as well as a polished thin section; DChenin holds the main mass.