The crystal structure of a Franklin, New Jersey, blue, Cu-bearing vesuvianite, commonly referred to as cyprine, was determined. The sample of tetragonal space group P4/nnc had cell parameters of a = 15.532(3) and c = 11.776(3) Å. An R value of 4.22% was reached for 1520 unique reflections with (Fo) > 3σ (Fo).

Although the basic structure is the same as found in previous studies, there are some significant differences. The Franklin vesuvianite shows Jahn-Teller distortion of Cu2+ in the B position, the irregular fivefold site on the c axis, with elongation along the c axis, the B-O(1O) direction, and compression in the B-O(6) direction. In addition, both oxygens not bonded to Si, O(10) and O(11), are hydroxyls.

The formula of the Franklin vesuvianite can be written
2[(Ca18.28Mn0.68)Al4Fe0.29Cu0.71)(Al6.36Mg0.56Ti0.03Zn0.97)(Si17.51Al0.49)O68(OH8.5F1.5)].
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