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Triclinic system, one of the structural categories to which crystalline solids can be assigned. Crystals in this system are referred to three axes of unequal lengths that are inclined at nonorthogonal (nonperpendicular) angles relative to each other.
If the atoms or atom groups in the solid are represented by points and the points are connected, the resulting lattice will consist of an orderly stacking of blocks, or unit cells. The triclinic unit cell has the least-symmetrical shape of all unit cells. Turquoise and other minerals such as microcline crystallize in the triclinic system.
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mineral: Symmetry elements…in both the monoclinic and triclinic systems. In the monoclinic system, two axes intersect one another at an oblique angle and lie in a plane perpendicular to the third axis; in the triclinic system, all axes intersect at oblique angles.…
clay mineral: Kaolin-serpentine group…is electrostatically neutral and has triclinic symmetry. Oxygen atoms and hydroxyl ions between the layers are paired with hydrogen bonding. Because of this weak bonding, random displacements between the layers are quite common and result in kaolinite minerals of lower crystallinity than that of the triclinic kaolinite. Dickite and nacrite…
feldspar: Crystal structure…so; the plagioclase feldspars are triclinic. All, however, have the same fundamental structure: it consists of a continuous, negatively charged, three-dimensional framework that is made up of corner-sharing SiO4 and AlO4 tetrahedrons (each tetrahedron consists of a central silicon or aluminum atom bonded to four oxygen atoms) and positively charged…