TSCHERMAK G. (1885) Die mikroskopische Beschaffenheit der Meteoriten (Stuttgart E. Schweizerbart'sche Verlagshandlung, E. Koch, 23 pp.). English Translation: The Microscopic Properties of Meteorites, Vol. 4, No. 6 (Smithsonian Contributions to Astrophysics, Washington, D.C., 1964).
Translation by J.A. Wood and E.M. Wood Shergotty, which I described several years ago (Tschermak, 1872b), should also be included with the eucrites. It is a conspicuously granular rock consisting essentially of dull yellow-gray grains and prisms, which were found to be augite, and water-clear glassy grains and laths. The latter resemble no known mineral; I named this material maskelynite. By incident light, the augite resembles volcanic augite. It is light brown and almost free of inclusions. Simple twinning ... is common. The augite has an unusual turbid appearance, visible by both incident and transmitted light. This is caused by very fine irregular cracks, which indicate that the augite has undergone a mechanical transformation. It differs from terrestrial augite in this respect, as well as in its chemical composition, being poorer in lime (CaO). The maskelynite is absolutely colorless and clear. In thin-section it usually occurs in elongated forms with fine lines parallel to their length, so that by ordinary light it looks exactly like plagioclase. Its chemical composition corresponds to a plagioclase of the labradorite series; but by polarized light it remains completely dark, proving that it is simply refracting. Cracks in the maskelynite are conchoidal*, like fracture surfaces in a glass. Maskelynite therefore has the properties of labradorite that has been transformed into an amorphous state by remelting or by a purely mechanical transformation. Inclusions in the maskelynite are common. They are quite irregular in form and consist of augite and magnetite. Cloudy white particles, a form of maskelynite, are visible here and there in Shergotty. A yellow silicate, optically biaxial, is present in small grains, but is very rare. Two opaque constituents have been recognized. One is magnetite, which was first found to be a meteoritic mineral in Shergotty; the other is very rare pyrrhotite. * conchoidal = noting a shell-like fracture form produced on certain minerals by a blow (Random Webster's Dictionary). Best wishes, Bernd ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
