The transition from alluaudite- to wyllieite-type phosphates: which is the role really played by aluminium?

Abstract

Keywords: AFM-STM studies of minerals and glasses, supramolecular structures, Fourier TransformStudy of the noncrystalline solid carbon, which is responsible for the most essential properties of Precambrian shungite rocks (shungite occurrences in the north-western part of the lake Onega, Karelia, Russia), is of interest because of a number of its physic-chemical properties underlying its many perspective applications [1]. Shungite carbon has graphite-like structure at the atomic level, but high-temperature treatment of the carbon does not lead to its graphitization. Basic structural elements is globule. Shungite globule is a spherical or ellipsoidal multilayer carbon formation, about 10 nm in size. Nature of these globules is supposed to be fullerene-like. Due to appeared to the present time to high-resolution scanning probe microscopic methods difficulties with visualization nanometrical structural elements of metastable natural substances are removed [1,2]. We applied scanning tunneling (STM) and atomic force (AFM) microscopes. for study highly-carbonaceous (to 98%) shungite carbon from various deposits, which different pressure -temperature of formation are characterized [1]. The supermolecular globular structure is concerned with to genetic features of substances, first of all with pressure -temperature and features of material composition of mineral formation environments. As one of the basic regulation of the supermolecular constitution of the investigated substances logarithmically normal distributions of structural elements on the sizes can be distinguished. Such character of distribution can speak that visualized supermolecular elements are aggregates of colloidal particles. The following step in research of supermolecular constitution is the structural-morphological analysis of images to reveal elementary form of the ordering expressing in a periodic arrangement of structural elements. As a whole it reveals diffraction analysis the analogue of which is Fourieranalysis in our case. Fourier Transformation has confirmed visually observed absence of a regularity in a relative location of elements of supermolecular structures, however has allowed to reveal the presence morphological analysis of researched substances in a number of samples statistically noted directions it testifies to occurrence presence of original superstructures ordering. Possible mechanisms of aggregations of shungites globules were analyzed.[1] Buseck P.R., Galdobina L.P., Kovalevski V.V., Rozhkova N.N., The wyllieite group of minerals consists of Na-Mn-Fe-Albearing phosphates which exhibit a crystal structure topologically similar to the alluaudite structure. However, the ordering of cations in the wyllieite structure induces a splitting of the M(2) and X(1) sites of alluaudite into the M(2a) M(2b) and X(1a) X(1b) positions. Consequently, the C2/c space group of alluaudite transforms into P2 1 /n in wyllieite, with no significant change of the unit-cell parameters, and with a structural formula which corresponds to X(2)X(1a)X(1b)M (1)...