FOUR CORNERS


Iron, IAB complex, Udei Station grouplet
standby for four corners photo
Found ~1923
36° 51' N., 108° 51' W.

A mass of 25 kg was found 24 km SE of the common corner of New Mexico, Arizona, Colorado, and Utah, but the find location is given as New Mexico. The meteorite was acquired by a geologist in 1923, but he failed to report any further details before his death in that year.

The metal in Four Corners has a small-grained, polycrystalline structure, exhibiting independently oriented Thomson (Widmanstätten) structures. Chondritic, angular silicate inclusions composed of grains of enstatite, diopside, olivine, and plagioclase up to 20 mm wide make up 15% of the meteorite by area. Graphite is present throughout and occurs as crystals of cliftonite in troilite and kamacite, as rims around silicate grains, and as graphite patches containing amorphous carbon.

In a study of the microstructure of the Four Corners meteorite, Holness et al. (2012) ascertained a mixing sequence for the metallic and silicate components. Early differentiation processes resulted in immiscible separation of FeNi-metal and FeS liquids. This process was interrupted by a catastrophic impact resulting in the shock-induced infiltration of angular silicate fragments by FeS to form troilite veins and inclusions. At the same time, large-scale mixing of these silicates led to their incorporation into still molten FeNi-metal, quenching the combined assemblage. Other silicates remained unmixed to become the meteorites of the winonaite group.

Four Corners is a medium octahedrite of the IAB iron-meteorite complex (Wasson and Kallemeyn (2002). The K–Ar closure age was calculated to be 4.50 (±0.01) b.y. To learn more about the relationships within the IAB complex and among other iron chemical groups, click here. The specimen of Four Corners pictured above is an etched 10.3 g partial slice.

The painted number indicates this section was once part of the collection of the Institute of Meteoritics, University of New Mexico, under the curatorship of Lincon LaPaz. This specimen is published in two UNM catalogs, LaPaz (1965) and Lange, Klaus, LaPaz (1980) —Per Mike Bandli.