A relatively fresh meteorite weighing 36.67 g was found in Northwest Africa and subsequently purchased by J. Higgins in October 2016 from a dealer in Nouakchott, Mauritania. A sample was analyzed at the University of Washington in Seattle (A. Irving and S. Kuehner) and NWA 11187 was classified as an ungrouped achondrite that has mineralogical and geochemical affinities to the ureilite group.
Northwest Africa 11187 is a coarse-grained achondrite consisting of large poikilitic grains of pigeonite enclosing small chadacrysts of Cr-poor forsteritic olivine (Irving and Kuehner, MetBull 106). Neither the Cr-poor olivine nor the poikilitic texture are typical for ureilites, although poikilitic clasts have previously been observed (e.g., polymict ureilite NWA 1926; T.E. Bunch, 2005). Graphite and kamacite are present in NWA 11187 as minor constituents.
An oxygen isotope analysis was conducted for NWA 11187 at the University of New Mexico (K. Ziegler), and the values plot near the CCAM line near the resolved field for ureilites (see the oxygen three-isotope plot). An in-depth study of multiple samples from the acapulcoitelodranite clan was conducted by Li et al. (2018), with the ungrouped achondrite NWA 11187 also included in the study. Utilizing a coupled Δ17O vs. ε54Cr (ε54Cr = 0.85 [±0.11]) diagram, they demonstrated that while NWA 11187 does plot among the broad field of the ureilites, it is also close to the compositionally diverse members composing the acapulcoitelodranite clan (see diagram below).
click on image for a magnified view
Diagram credit: Li et al., GCA, vol. 242, p. 92 (2018)
'Evidence for a Multilayered Internal Structure of the Chondritic AcapulcoiteLodranite Parent Asteroid'
Northwest Africa 11187 shows evidence of low shock and a low degree of terrestrial weathering. The main mass of this meteorite resides in the Royal Ontario Museum. The specimen of NWA 11187 shown above is a 0.25 g partial slice that was taken from the ~1 g slice shown below.