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13.6.3: Complex Atomic Arrangements

  • Page ID
    18360
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    Silicate crystal structures may be complex. Many silicates contain anions or anionic groups other than O2−. Muscovite, for example, contains (OH) and has the formula KAl2(AlSi3O10)(OH)2. Other silicates, such as kyanite, and titanite, CaTi(SiO4)O, contain O2- ions unassociated with the (SiO4)4- tetrahedra. In muscovite and many other minerals, aluminum is in both tetrahedral and octahedral coordination. Still other silicates do not fit neatly into a subclass. Zoisite, Ca2Al3O(SiO4)(Si2O7)(OH), contains both isolated tetrahedra and paired tetrahedra. (It also contains oxygen not in tetrahedra.) Some mineralogy texts and reference books separate elements and include extra parentheses in mineral formulas (as has been done in this paragraph) to emphasize the nature of the atomic arrangement, but often we omit such niceties for brevity. In shorter form, we can write muscovite’s formula as KAl3Si3O10(OH)2; kyanite’s becomes Al2SiO5; titanite’s becomes CaTiSiO5; and zoisite’s becomes Ca2Al3Si3O12(OH). While being shorter and, perhaps, easier to write, these formulas give little hint of crystal structure.


    This page titled 13.6.3: Complex Atomic Arrangements is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Dexter Perkins via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.