Kilchoanite Ca3Si2O7 is a polymorph of rankinite, which is a true sorosilicate. Kilchoanite, on the other hand, has three-tetrahedra units and solitary tetrahedra.
The structure turns out to be pretty simple. Above is a view looking face on at the silica units. Calcium atoms are yellow. All the atoms in the structure line up directly behind one another.
Above, a slightly oblique view showing how everything lines up neatly. Darker colors are closer to the plane of the diagram.
Above, an end-on view. Trimers (triple units) are purple and single tetrahedra are blue. Darker colors are closer to the plane of the diagram.
This is a nice illustration of a mineral where coordination polyhedra don't help. Above is a face-on view with silica tetrahedra in violet and calcium polyhedra in other colors.
Created 22 April 2013, Last Update 08 Jul 2013
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