VERMILLION

A 34.36 kg mass was found by M. and G. Farrell while planting in a grain field in Marshall County, Kansas, in the vicinity of the Black Vermillion River. This was purchased by a dealer with the belief that it was a Brenham mass. Upon cutting, it was discovered to be unique from Brenham. Vermillion consists of 86 vol% FeNi-metal and 14 vol% silicates with grains much smaller than normal.

Subsequent studies found that Vermillion shares a similar pyroxene composition, mineralogy, O-isotope composition, and REE pattern with the pyroxene-containing pallasite Yamato 8451, and these two were tentatively recognized as members of a new pyroxene-pallasite grouplet. However, significant differences between the two are not resolved, including differences in texture (Y-8451 contains 4× the vol% of silicates as Vermillion) and siderophile trace element composition, as well as the presence of the carbide cohenite in Vermillion. On a Ni–Au diagram, Vermillion plots just outside of the low-Au end of the IAB main group irons, and also plots along an extention of the low-Au, medium-Ni (sLM) subgroup into lower Au compositions (Wasson and Kallemeyn, 2002). Furthermore, the O-isotopic composition of Vermillion is within the range of IAB irons, and therefore, Vermillion may be more confidently considered to be genetically related to members of the low-Au division of the IAB iron-meteorite complex.

Both of these pyroxene-bearing meteorites contain low- and high-Ca pyroxenes that occur either as large grains, as inclusions in olivine, or as grains bordering olivine. Pyroxene accounts for ~0.7 and ~1.6 vol% of the silicate fraction of Vermillion and Y-8451 respectively, the remainder being mostly olivine. By comparison, the main-group pallasites contain all olivine with only trace amounts of pyroxene. This may indicate a lower crystallization temperature for these pyroxene-bearing meteorites.

The olivine fayalite composition of these pyroxene-bearing pallasites plots at the magnesian end of the main-group pallasite range. As a comparison, the Eagle Station pallasite grouplet has the most ferroan composition, as well as a high Ge/Ga ratio in the metal and a unique O-isotope composition. The high Ir content in the Eagle Station pallasites suggests crystallization from the inner core region of its parent body, below the core–mantle interface in which the main-group and pyroxene-bearing meteorites probably formed on their respective parent bodies.

Siderophile trace element and oxygen isotopic compositions clearly resolve these pyroxene-bearing meteorites from the main-group and Eagle Station pallasites. Therefore, Vermillion and Yamato 8451 represent at least one other parent body on which pallasite-like textures were formed. More recently, a 46 g pyroxene-rich pallasite named Zinder was found in Niger in 1999. It contains 28 vol% pyroxene and 27 vol% olivine in a network of FeNi-metal. Additionally, in 2003 a 53 g pyroxene-rich pallasite named NWA 1911 was purchased in northwest Africa. It has a modal composition of about 24% FeNi-metal and 75% silicates, with the silicates consisting of 34.5% orthopyroxene and 40.2% olivine. Further studies may help to elucidate the relationship between these diverse silicate-bearing meteorites. The specimen of Vermillion pictured above is a 67.9 g partial slice. Below is a close-up of the etched reverse side.

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