Julesburg meteorite, Sedgwick County, Colorado, USAi

Regional Level Types
Julesburg meteorite	Meteorite Fall Location
Sedgwick County	County
Colorado	State
USA	Country

Ordinary chondrite, unequilibrated (L3.6; S3; W1.5)
Found, 1983; 57.9 kg

A single mass discovered by a farmer was discarded and later found in a Julesburg city landfill. The meteorite's original fusion crust was nearly intact with one face particularly well-pitted. Some thiner 'secondary' crustal areas suggest that at least 3 smaller fragments had spalled off during atmospheric entry. Closer inspections revealed distinct chondrules, chondrule fragments, and xenoliths within an unequilibrated gray and brown matrix. Compositionally, a sharply defined olivine peak (Fa22.6), a crude Ca-poor pyroxene 'median' Fs~18-20, Co in kamacite, and bulk iron (~21 wt.%) are characteristic of the L-chondrite geochemical group. However, the olivine and Ca-poor pyroxene compositions are quite variable (Fa1-25; Fs3-23, resp.), consistent with its L3.6 petrologic type. Mineralogically the meteorite consists primarily of olivine and pyroxene along with minor troilite, feldspathic material, and Fe-Ni metal. Plagioclase in both inclusions and chondrules is quite variable with both anorthitic and albitic regions and grains (bytownite plagioclase is, however, most prominent). Accessory chromite and spinels are among other minor silicates, sulfides, and oxides reported. Unusual O-16 rich regions and pre-solar phases such as diamonds, graphite, and SiC have also been reported. Pervasive instances of small glassy regions of various colors and compositions are found in the matrix and, especially, in chondrule mesostasis. In addition to the usually minor limonite stains on the meteorite's crust and in thin sections, occasional veins of hydrated weatherates penetrate deep into interior portions. Helium and argon gas retention age of ~1.6 and 1 Ga, respective, may reference major impacts in the long journey from an original parent body to daughter asteroid to an eventual earth-crossing meteoroid which eventually became the Julesburg meteorite with its anomalous inclusions and exotic isotopic ratios.

The L group of ordinary chondrites (relatively low in total iron) chondrites are the largest group of witnessed meteorite falls constituting ~40 of all well-described falls. However, petrologic type L3 chondrites are a much smaller subset of the total L-group and represent ~1.5% of all witnessed falls and ~4% of all recovered meteorites. Julesburg itself is by far the most massive of the 55 ordinary chondrites classified as exactly 'L3.6' and currently listed at the Meteoritical Bulletin Database as of late February 2017. Khohar, an Indian fall [9.7 kg], is the 2nd most massive recovered L3.6 meteorite to date.

The main mass has been with the American Meteorite Laboratory (Denver). Moderate masses in the 500-2000 g range were distributed at the Natural History Museum (London), Naturhistorisches Museum (Vienna), the Monnig Collection (Fort Worth), and Arizona State University.

Beyond this report — The somewhat brief review by A.L. Graham (1993) cited below provides an excellent introductory framework for more technical excursions into the rich exotica found within this mineraliferous and very texturally diverse meteorite.

Other Regions, Features and Areas containing this locality

References