The Ordovician chondrite from Brunflo, central Sweden, I. General description and primary minerals

Abstract

The Brunflo chondrite was found in the Rödbrottet quarry near Brunflo, central Sweden (lat. 63°5′N, long. 14°53′E). The meteorite (ca. 11 cm × 9.5 cm) occurs in a polished slab of Middle Ordovician limestone which, based on its content of conodonts, belongs to the Aserian Segerstad Limestone. The meteorite fell in the Iapetus Ocean, close to its eastern coast line. The original minerals, except chromite, are replaced by secondary minerals, mainly calcite. Remarkably, even minute details of textures and structures are preserved in some areas. The various types of chondrules and their frequencies could therefore be studied. They are similar to present falls of ordinary chondrites of petrologic types 3 and 4. Chromite occurs as up to ca. 0.1 mm large grains. Microprobe analyses of 59 grains show that, except for Zn, the composition is fairly constant and similar to H4–H5 chromites. The Zn content varies from 0.2 to 6.8 wt.% ZnO, mean ca. 0.6 wt.%. Two analyses show that also chrome spinel is present. Tentatively Brunflo is classified as H4–H5.