Larned        38º 11.97’ N, 99º 9.72’ W

Kansas, United States

Find: 1977

Achondrite (aubrite, anomalous)

History: Found by an anonymous landowner on his farm in 1977, about 1 mile north and 4 miles west of Larned, Kansas. The mass was brought to the Big Well in Greensburg, Kansas in April 2007 and purchased by Dr. Donald Stimpson.

Physical characteristics: A single mass weighing 28.1 kg surrounded by grayish to brownish, shaley weathering rind. The interior is mostly gray with metal visible in places, and it is transected by anastomosing, thin, dark brown veinlets.

Petrography: (A. Irving and S. Kuehner, UWS; T. Bunch and J. Wittke, NAU): Polymict breccia composed mostly of large metal-poor clasts, but with locally abundant metal in the matrix. The major phase is near-pure enstatite (up to 1.2 cm, many exhibiting abundant fractures, mosaicism, and planar deformation features), with accessory diopside, schreibersite, sodic plagioclase glass, silica, Cr-bearing troilite, daubreelite, niningerite, Si-bearing kamacite, and rare taenite. One 1.4 x 1.0 mm clast is a websterite composed of 52 vol% enstatite, 40 vol% diopside, and 8 vol% schreibersite and sulfides (including an iron sulfide phase compositionally similar to greigite). Silica exhibits ballen structures and occurs as inclusions in enstatite and is locally abundant in the matrix. Secondary veinlets are composed of a hydrous iron silicate compositionally similar to greenalite.

Geochemistry: Enstatite (Fs_0.1–0.2Wo_0.4–1.1), diopside (Fs_0.2Wo₄₇), plagioclase glass (~Ab₇₉Or₂₁), kamacite (Si 1.35–2.2 wt%, Ni 5.9–6.6 wt%), taenite (Si 1.1 wt%, Ni 12.6 wt%).

Classification: Achondrite (aubrite, anomalous). This large specimen contains more metal and more silica polymorph than most aubrites, and has experienced a high degree of shock (producing fractured enstatite, ballen silica and feldspathic glass).

Specimens: A total of 190 g of sample and two polished thin sections are on deposit at UWS. The main mass is held by DStimpson.