Several Silicates, Zircon, and Beryl

A simple count of the number of comer to comer distances across the tetrahedra in the jc-direction (horizontal) is 1/2 + 1 + 1/2 = 2. The count in the y-direction (vertically) is the same. Hence, the a- and b-axes are equal in length, but not equal to the c-axis. 

Our final example of the effect of the anion on the symmetry of the unit ceU (and consequently the symmetry of the crystals that are formed) is the mineral beryl. Beryl contains a cyclosilicate ion. 

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