Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Sapphirine (Mg,Al)8(Al,Si)6O20 is a metamorphic mineral. It consists of branched single chains of silica tetrahedra (purple) and aluminum tetrahedra (blue). Aluminum octahedra (yellow) link the chains.
Below: The silica chain layers alternate with layers of aluminum (yellow) and magnesium (green) octahedra.
The sapphirine structure is approximately close-packed. Above is a silica-aluminum layer with one plane of oxygen atoms indicated in blue. Below is a magnesium-aluminum octahedra layer with two planes of oxygen atoms. Atoms further from the plane of view are lighter. In both views the polyhedra are shown in light colors.
Below: Diagram showing how the silica and octahedral layers connect.
Below: view down the  zone, showing the pseudo-rhombic structure. Background polyhedra are lighter.
Below: view down the c-axis, showing alternation of the octahedral and tetrahedral layers.
Below: view down the a-axis, showing the approximate close-packed structure. Octahedra are yellow and green, tetrahedra are purple and blue.
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Created 22 April 2013, Last Update