Mineralogy of Phyllosilicates and Tectosilicates
The silicate subgroups of phyllosilicates and tectosilicates include minerals used in industry and jewelry. Learn how to identify them.
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Crystal Chemistry of Phyllosilicates and Tectosilicates
Phyllosilicates and tectosilicates are comprised of numerous mineral groups and important mineral species. The most well-known phyllosilicates are talc, micas, serpentines, and clays. Tectosilicates include quartz and numerous quartz modifications, as well as the extensive feldspar family, feldspathoids, and zeolites.
Introduction to Phyllosilicates
Most rock-forming phyllosilicates are made up of infinite two-dimensional layers. Phyllosilicates are sometimes called “sheet” or “layered silicates” in reference to their layered structure and their sheet or scale-like mineral forms. The structural unit of phyllosilicates is [Si4O10]4- (sometimes written as [Si2O5]2- — as the structural unit divided by 2).
Phyllosilicate sheets or layers are not identical within one mineral. Rather, they alternate between layers of octahedral and tetrahedral atomic structure. As a result, phyllosilicates are further subdivided into:
- 1-layer silicates, where all layers are similar (for example, apophyllite (KCa4[Si4O10]2(F,OH)2⋅8H2O))
- 2-layer silicates (for example, kaolinite (Al4[Si4O
Olena Rybnikova, PhD
Olena Rybnikova is a gemologist and mineralogist. She has a PhD in mineralogy and petrology specializing in beryllium minerals and is a certified Applied Jewelry Professional accredited by the Gemological Institute of America. Her passion is actively promoting knowledge and appreciation of nature, geology, and gemstones.
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