Polymineral Biomorphoses in Basal Skeletons of Hypercalcified Sponges and Fusulinid Shells from the Gzhelian Stage of the Moscow Basin

This paper describes the mineral composition and structure of smectite, goethite, chalcedony, and sanidine biomorphoses over calcite sponge skeletons and fusulinid shells. The newly formed minerals, except for chalcedony, did not replace the calcite of the fossil skeletons, but formed enveloping biomorphoses in the form of 5–10 μm thick rims on the surface of cavities and spicules in sponge skeletons and chamber walls in fusulinid shells. The resulting mineral structures, predominantly smectite in composition, were absent from sponges and fusulinids during their lifetime. The biomorphoses extracted from fossils by processing the latter with a weak acetic acid reproduce in great detail many morphological details of the internal structure of the skeletons of fossil organisms.