Analcime is variously classed as a feldspathoid or zeolite, with the formula NaAlSi2O6ĚH2O. It has a nearly cubic unit cell about 1.37 nm on an edge, and crystallizes with pseudocubic crystal forms. The actual symmetry depends on the ordering of Si and Al tetrahedra, and can be any class except hexagonal, though the unit cell is always very nearly cubic.
Above, view down the c-axis. Silica tetrahedra are purple, aluminum is yellow, sodium atoms are orange and water molecules (oxygen atoms) are blue. Background atoms and tetrahedra are lighter in shade. Hidden water molecules are outlined in gray.
Above: view normal to the c-axis. Apart from the ordering of the aluminum tetrahedra, the structure is the same as the view down the a-axis.
Above: view of a single layer of tetrahedra. The layers are identical but differ in aluminum-silica ordering and relative placement. As befits the near-isometric symmetry, layers are identical in all axis directions.
Created 22 April 2013, Last Update 01 Jul 2013
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