Garnettirakenne

Garnettirakenne refers to the crystal structure adopted by minerals of the garnet group. This structure is characterized by a cubic symmetry and is typically represented by the general chemical formula X3Y2(SiO4)3. In this formula, X represents divalent cations, commonly calcium, magnesium, ferrous iron, or manganese, which occupy the dodecahedral sites. Y represents trivalent cations, such as aluminum, ferric iron, chromium, or titanium, which occupy the octahedral sites. The tetrahedrally coordinated sites are occupied by the silicon-oxygen tetrahedron, (SiO4).

The garnet structure is built from corner-sharing SiO4 tetrahedra and isolated octahedra (YO6) and dodecahedra (XO8). These polyhedra are arranged in a specific three-dimensional framework that imparts significant stability to the mineral. The arrangement results in a relatively open structure with channels that can accommodate interstitial atoms or molecules, although this is less common in natural garnets.

Minerals with the garnettirakenne exhibit a wide range of physical properties, including hardness, refractive index, and color, depending on the specific chemical composition. Despite variations in composition, the fundamental structural arrangement remains consistent. This structural motif is found in a variety of economically important minerals, including almandine, pyrope, spessartine, grossular, and andradite, each representing a different end-member of the garnet solid solution series. The stability and robustness of the garnettirakenne make these minerals common in metamorphic rocks, but they are also found in igneous and sedimentary environments.