International scientific journal

ISSN: 2663-0419 (electronic version)

ISSN: 2218-8754 (print version)

International scientific journal

ISSN: 2663-0419 (electronic version)

ISSN: 2218-8754 (print version)

SCImago Journal & Country Rank

Structural hierarchy of Ca- and TR- triorthosilicates and their derivatives

Shirinova A.F., Chiragov M.I.

Crystallography, mineralogy and geochemistry department, Baku State University 23, Acad. Zakhid Khalilov str., Baku, Azerbaijan, AZ 1148:


It is known that physical and chemical properties and paragenetic peculiarities of minerals are related to their crystalline structure. The hierarchical scheme of mineral structure re-search shows that classification according to chemical composition does not give a complete picture of the minerals’ properties. Taking into account the well-known works of M.I.Chiragov and F.C.Hawthorne on the structural classification of minerals, the structures of Ca- and TR-triortosilicates and their derivatives are considered for the first time in this paper using the comparative crystal chemistry method and structural hierarchy. The structural hierarchy of minerals is based on the primary polymerization of different type coordination polyhedra which results in formation of the parent structural minals or clusters. Taking into account the symmetry of triorto-silicates and the form of polymerisation of tetrahedrons with Ca- and TR-octahedrons, four types of clusters with different configurations and chemical compositions have been identified: |M(Si3O10)(H2O)3|, |M(Si3O10)2|, |M(Si3O10)(H2O)4| and |M(Si3O10)2(H2O)2|. Depending on the shape of clusters polymerization, a hierarchical scheme for the formation of structural types of Ca- and TR-triortosilicates and their derivatives is presented. This results in the formation of structural blocks and mixed frames with calcium atoms in Ca-silicates and sodium or potassium atoms in TR-silicates. According to the chemical composition and shape of silicon-oxygen radical, such minerals as delhayelite and macdonaldite are included in one group. According to the structural classification with the extraction of clusters, it was found out that the structures of these minerals are formed from two different configurations of minals and, consequently, as a result of their polymerization, different structural types are formed. The substantiation of the structural hierarchy is reflected in the conditions of formation of the group of minerals delhayelite and macdonaldite. The formation of dolchayelite is associated with the high-temperature stage of pegmatite formation at the stage of entry of potassium-rich metamorphosing solutions. Hydro-delhayelite is a product of hypergenesis and hydrothermal change of delhayelite. Under these conditions the removal of sodium, partially potassium and all fluorine and chlorine takes place. The structural type of mac-donaldite is associated with low temperature stage of pegmatite formation or with late hydrothermal stage of mineral formation. In all cases, however, the medium must be highly alkaline and calcium-rich for the macdonaldite structural type or rich in rare earth cations for the monterejianite structure. These structural features are tested indicators for mineral formation processes.

Keywords: Ca- and TR- triorthosilicates, clusters, structural units, structural blocks, formation of structures



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DOI: 10.33677/ggianas20200200047