Northwest Africa 16297 (NWA 16297)

(Northwest Africa)

Purchased: July 2020

Classification: Ordinary chondrite (H3)

History: Mr. Jasper Spencer purchased a single 58 g stone from a Mauritanian dealer in July 2020 via FB Messenger, and sent a 14.7 g end cut to Cascadia for classification

Physical characteristics: Physical Characteristics: Exterior of end cut shows dark brown remnant fusion crust. Interior cut faces show closely-packed, well-defined chondrules and an abundance (~10% surface area) of metal between and surrounding chondrules.

Petrography: (M. Hutson, A. Ruzicka, Cascadia): Chondrules are well-defined and often partially surrounded by inclusion-filled metal and troilite; inclusions are typically grains of olivine, low-Ca pyroxene, and phosphate minerals (merrillite and chlorapatite). Chondrule mesostasis consists of crystallite-bearing feldspathic glass. Commonly, rims of more calcic pyroxene (pigeonite and augite) form boundaries between low-Ca pyroxene and feldspathic mesostases. A notable feature of the meteorite is the abundance of a silica polymorph, often associated with iron-rich, reversely-zoned chondrules or chondrule fragments composed of fine-grained low-Ca pyroxene. Silica polymorph also forms masses that substantially fill a few chondrules.

Geochemistry: Olivine (Fa_17.6±2.5, range Fa_3.1-20.3, N=78), low-Ca pyroxene (Fs_15.7±10.1Wo_1.2±1.1, range Fs_2.4-37.5Wo_0.3-4.8, N=70).

Classification: Ordinary chondrite (H3) based on texture and mineral chemistry.

Specimens: Cascadia holds 9.6 g in three pieces, as well as a polished thin section and material in an epoxy butt; Mr. Jasper Spencer holds the main mass.