widmannstättian

from The Century Dictionary.

• Pertaining to Aloys Beck von Widmannstätt, of Vienna (1753–1849)
• figures, the name given to certain peculiar markings seen on the polished surfaces of many meteoric irons (siderolites) when these have been acted on by an acid. They were first noticed by Widmannstätt in 1808, on the Agram meteorite. The general appearance of these markings may be learned from the annexed figure, which is a copy of a photograph, of natural size, of a part of an etched section of the Laurens county (South Carolina) meteoric iron. The Widmannstȧttian figures are sections of planes of cleavage or of crystalline growth, along which segregation, or chemical change of some sort, has taken place, and whose form and position with reference to each other are in accordance with the laws governing the development of crystalline substances belonging to the isometric system. Reichenbach divided these figures into what he called a trias (more properly a triad)—namely, kamacite (Balkeneiseu), tænite (Bandeisen), and plessite (Fülleisen)—the first consisting, so far as has been as yet made out, of distinct plates of iron, with a comparatively small percentage of nickel; the second consisting of thinner plates enveloping the kamacite, and richer in nickel; and the third being a sort of ground-mass filling the cavities, and having less obvious indications of structure and generally a darker color than the others. It has frequently been stated that some meteoric irons do not exhibit the Widmannstättian figures, and that consequently their absence is not a proof of non-celestial origin; it is certain, however, that few, if any, siderolites do not show traces of some kind of structure, although investigators in this branch of science are by no means agreed as to what kind of figures are properly designated by the name Widmannstättian. A somewhat similar uncertainty prevails with regard to the figures developed by etching on the terrestrial iron of Ovifak; so that, at the present time, it cannot be said that the Widmannstȧttian figures furnish a positive criterion by which the authenticity of a meteoric iron may be established; yet it is certain that welldeveloped figures of this kind do render it highly probable that the specimen in which they are seen is extraterrestrial. A classification of meteoric irons on the basis of the different forms of figures which they exhibit, in the present condition of this branch of science, does not seem to be justifiable, although this has been attempted.