A metallographie study of some iron meteorites of high nickel content

Abstract

Summary A metallographic investigation of macro- and microstructure, supported in some instances by microprobe examination, has been made on a number of nickel-rich iron meteorites from the British Museum Collection. Monahans, Wiley, Cowra, and Deep Springs are considered together as plessitic irons rather than ataxites, whilst Morradal shows an unusual and coarse plessitic structure that has been altered by pre-terrestrial shock and reheating. Cape of Good Hope, Hoba, Tlacotepec, and Chinga show chemical and structural similarities and are discussed together, as are Weaver Mountains, Klondike, and Warburton Range. Meteorites considered separately include Kokomo, Piñon, Shingle Springs, South Byron, San Cristobal, Lime Creek, and Santa Catharina. Particular attention is paid to the presence of sulphides and of phosphorus-containing phases and their influence on the formation of the macro- and microstructure of these meteorites. Patches of oriented sheen form a macroscopic feature of the Cape of Good Hope group of irons and this effect is considered in relation to details of the microstructure. Attention is drawn to the fact that in Cowra, Piñon, Weaver Mountains, South Byron, and Morradal the troilite appears to have been remelted and dispersed by a shock event that operated at a temperature sufficiently high to allow obvious shock damage to anneal out of the metal phases.