Images of Vienna IVA with an overview (top) of the main mass and a closeup (below) showing flowlines that formed during atmospheric entry. Credit: UW Geology Museum.
Image of the etched cross section of the Vienna type specimen. Credit: Field Museum.
Backscattered electron image (left), iron and nickel maps (center) and nickel concentration profile (right) of a taenite band in the type specimen of Vienna. Credit: Field Museum.

Robert A. Pritzker Center Classifies Rare Iron Meteorite

The Robert A. Pritzker Center at the Field Museum has recently classified a new iron meteorite, discovered in Vienna, Wisconsin as an IVA iron meteorite. This is the second meteorite classified by the Pritzker Center from the US Midwest found near a small town sharing its name with a major European city, following the Hamburg meteorite.

IVA iron meteorites are exceptionally rare, representing only about 1 permill of all known meteorites and about 7% of all known iron meteorites.

Details of the Discovery

Physical Characteristics

The meteorite is an oriented mass resembling an irregular pyramid, well-sculpted with regmaglypts and flow lines on the leading surface, and some rollover lipping. The exterior, although oxidized and flaking, is only weathered less than 1 mm deep. The interior remains mostly non-oxidized, except for some peripheral areas. The Widmanstätten pattern, revealed on a polished and etched cross-section, shows an average bandwidth of 0.27±0.07 mm, characteristic of IVA irons and fine octahedrites.

A Meteorite’s Journey to Discovery

On a balmy spring day in May 2009, farmer Jim Koch's plow unearthed an unusually hefty rock while preparing a field for alfalfa in the Town of Vienna, just north of Madison. Initially unnoticed, the knobby rock caught Koch’s attention during a routine stone-picking walk across the freshly tilled soil.

“I’m thinking, ‘this is quite heavy,'” Koch recalled. “It was uniquely different and caught my attention.”

Koch had discovered a meteorite, and not just any space rock: It’s the largest iron meteorite classified in the United States since 1981. Weighing nearly 110 pounds, it is Wisconsin’s 15th classified meteorite and the first ever recorded in Dane County. The meteorite bears rare features for an iron meteorite, including scars from its fiery entry through Earth's atmosphere, etched into its surface just before it crashed on what would become Vienna EqHo Farm. Here, Koch and his wife, Jan Shepel, raise dairy cattle and horses.

The rock sat for years in an outbuilding on Vienna EqHo Farm, protected under a pile of old carpeting. After some years, a sample of the meteorite was sent to the Field Museum of Natural History in Chicago, where it was officially confirmed as a meteorite. The main mass resides at the University of Wisconsin Geology Museum in Madison.

The classification was performed by Philipp Heck with help from Jim Holstein, Noriko Kita, Carrie Eaton, and Richard Slaughter. Philipp Heck acknowledges help from Laure Dussubieux for providing access to and help with the Field Museum’s Elemental Analysis Facility.

This discovery adds to the world-class meteorite collection at Field Museum’s Robert A. Pritzker Center which has a particular strength in iron meteorites.