Spherulites and spherulitic tactoids of anthraxolite

Abstract

A pebble of anthraxolite found in the basin of the Kendei River, a tributary of the Lena River, was examined under polarization metallographic and electron microscopes to get an insight into their structure and ontogeny. A polished section of the mineral demonstrates evident anisotropy in polarized reflected light and finely sculptured microrelief of growth and induction surfaces of spherulites on the fracture (fractograms). The morphogenetic inspection and study of ontogenetic signs of origination, growth, phase transformations, and other changes of anthraxolite revealed a growth mechanism typical of spherulitic dendrites owing to low-angle splitting of radial subindividuals. Layered gravity structures (‘mineralogical levels’) have been found in crystallization voids. They are composed of an ordered even-grained aggregate of spherical crystals of anthraxolite with the tactoid texture of precious opal. The tactoid mineralogical levels of anthraxolite are characterized by the block structure of microspherulite aggregates, signs of deformation, twinning and geometrical selection of blocks, and elements of recrystallization. Growth-oriented zones of regular nets with endotaxial inclusions of graphite inside the cells have been observed on induction surfaces in spherulitic dendrites. Their appearance is considered an indicator of phase transformations. Supramolecular structures and their effect on the morphology of anthraxolite are discussed in short.