NORTHWEST AFRICA 12774


Angrite
Basaltic/Quenched, Picritic
standby for nwa 12774 photo
Purchased June 2019
no coordinates recorded

A single, relatively fresh stone weighing 454 g was acquired from a Mauritanian dealer by R. and J. Chaoui and subsequently sold to M. Jost and K. Wimmer at the Ensisheim Show. A sample of the meteorite was analyzed at the University of Washington in Seattle (A. Irving) and at Washington University in St. Louis (P. Carpenter), and NWA 12774 was classified as a quenched, olivine-phyric angrite.

The meteorite has a porphyritic texture composed of compositionally-zoned skeletal olivine phenocrysts and Al–Ti augite phenocrysts arrayed in a black groundmass. The groundmass is very fine-grained and consists of anorthite, olivine, kirschsteinite, and Al–Ti augite, along with minor troilite and ulvöspinel and rare kamacite.

A limited number of unique angrites are represented in our collections today which can be grouped as basaltic/quenched, sub-volcanic/metamorphic, or plutonic/metamorphic, along with a single dunitic sample NWA 8535 (photo courtesy of Habib Naji). Another quenched angrite, NWA 7203 (photo courtesy of Labenne Meteorites), exhibits a striking variolitic texture. Portions of the angrite asteroid must be in a stable orbit (planetary or asteroid belt) from which spallation has continued to occur over the past ~56 m.y. as indicated by the broad range in angrite CRE ages.

Northwest Africa 12774 has a similar texture to the 46.2 g NWA 7812, but the two angrites are not paired (A. Irving and P. Carpenter, MetBull 108). The photo of NWA 12774 shown above is a 0.32 g part slice, while that below is an impressive 17.196 g full slice of this visually striking angrite, shown courtesy of Tom Stalder.

standby for nwa 12774 full slice photo
click on photo for a magnified view

Photo courtesy of Tom Stalder—Sahara Gems