Topaz (Al2SiO4(OH,F)2) is an aluminosilicate with one oxygen replaced by two hydroxyl or fluorine atoms. The structure consists of close-packed layers in an ABAC stacking. Zigzag aluminum octahedral chains are joined by silica tetrahedra. In the polyhedral models below, the red spheres denote hydroxyl or fluorine. The first model shows the zigzag chains, the second a larger piece of the structure.
The ball model below shows a single oxygen layer (blue) with aluminum (yellow) and silicon (purple) cations.
The ball model below shows several layers of the structure. Oxygen is shown in shades of blue, hydroxyl or fluorine in green, aluminum in yellow and silicon in purple.
Created 22 February, 2001, Last Update 14 December 2009
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