Abstract
Electron microscopic investigations (high resolution electron microscopy and dark field imaging) of oxyhornblencles revealed shapes, sizes of pyroxene phase, and structural relationships between the pyroxene and amphibole phases; oxyhornblendes from Ikenofukuro (Ikebukuro), Nagano Pref., and Eboshiyama, Niigata Pref., contain (010) pyroxene lamellae. The lamellae are usually very thin (several tens to 100 A, or more) and sporadically distributed in the specimens. The results of the observations were consistent with the previous estimation by TOMITA (1965) that the pyroxene and amphibole phases are arranged side by side on (010), sharing their three crystallographic axes, respectively. Amphibole specimens from several localities were heated at 900℃〜1050℃ in air and observed by electron microscopy. Very similar pyroxene lamellae were also observed in the heated specimens ("oxyamphiboles"). These pyroxene lamellae found in both oxyhornblendes and heated amphiboles ("oxyamphiboles") are topotacticaily and coherently intergrown on (010). The pyroxene lamellae with minimum width should be composed of 4 single chains that are transformed from 2 double chains. A variety of occurrences of fine pyroxene lamellae and the related textures were observed. Systematic observation of the heated "fibrous amphibole" specimens from Akatani mine represents the following process of the transformation; nucleation of pyroxene slabs → formation of the lamellar structure showing the alternation of pyroxene and amphibole structures → appearance of spotty decomposed domains → final almost completion of pyroxene structure with a little amount of isolated double chains and many spotty decomposed domains. The spotty decomposed domains may be regarded as donor regions proposed by FREEMAN and TAYLOR (1960) in which the structure decomposed and ractant materials are produced to form pyroxene structure in the neighbouring areas.
