Pallasite, PMG-am (main-group, anomalous metal composition)
35° 34' N., 105° 49' W.
Initially, three oriented, regmaglypted masses weighing 67, 52, and 24 kg were found in close proximity by Charles Sponsler on the ranch of Mrs. Roival near Canonçito, New Mexico, five miles south of Glorieta Mountain. Well-preserved black fusion crust is present, and the lack of secondary fusion crust on some surfaces is indicative of a late atmospheric breakup for the initial mass. Several additional large masses were subsequently recovered, and smaller masses from this shower continue to be found to this day, mostly within a strewnfield measuring 4 × 1 km. Many Glorieta specimens display a unique elongated, cylindrical or prismatic shape, complete with fusion crust and rare olivine crystals. A medium Thomson (Widmanstätten) structure is produced when etched.
Glorieta Mountain is an anomalous pallasite due to its significantly lower Ge and Ga content than that of main-group pallasites. Its elemental composition suggests that it was derived in large part from the late-stage core metallic melt component of the metalsilicate mixture. Glorieta Mountain has a cosmic-ray exposure age of 230 (±70) m.y. Curiously, its trace-element values and O- and N-isotopic compositions plot in the range of the IIICD-iron group. While most main-group pallasites contain troilite that averages ~2.4 vol%, the abundance of troilite in Glorieta Mountain is much higher, measuring 8 vol%; remarkably, the troilite content of Phillips County is extraordinarily high at >20 vol% (Boesenberg, 2010). Glorieta Mountain is among the pallasites with the lowest cooling rate, at 2.5 (±0.3) K/m.y., while the highest cooling rate of 18 (±9) K/m.y. is found in Finmarken (Yang et al., 2010). These two main-group end members are believed to have cooled at different depths on the same parent body.
A 128 g Glorieta fragment was found in a pottery bowl in an Indian ruin located ~50 km from the strewnfield displaying evidence that it might have been used ceremonially. A 40 g fragment, later identified as a Gloritta specimen, was found in a medicine pouch at the Nambe Pueblo in the 1930's (S. Schoner, pers. comm.). This perfectly preserved fragment was found along with artifacts that were dated to 1250 AD, suggesting that this pallasite may have been a witnessed fall from around this time period. The Glorieta Mountain specimen in the photo above is a 5.9 g nugget-like specimen exhibiting a smooth, fusion-crusted side and a rough, fragmented side revealing imbedded clusters of yellow-orange olivine crystals. The photo below shows a beautiful 164 g Glorietta slice with a striking etch pattern.
Photo by Marvin KillgoreSouthwest Meteorite Lab
Courtesy of Michael Masse