The nomenclature of CaZrTi 2 O 7 minerals has become very confused, such that zirconolite, zirkelite and polymignite each have acquired multiple meanings and represent five different crystal structures. To resolve these inconsistencies, the IMA approved resolutions as follows. Zirconolite is the non- crystalline (metamict) mineral or mineral with undetermined polytypoid of CaZrTi 2 O 7 . Zirconolite-3 O is the three-layered orthorhombic polytypoid of CaZrTi 2 O 7 . Zirconolite-3 T is the three-layered trigonal polytypoid of CaZrTi 2 O 7 . Zirconolite-2 M is the two-layered monoclinic polytypoid of CaZrTi 2 O 7 . Polymignite (metamict) is discarded as equivalent to zirconolite. Zirkelite is the cubic mineral with formula (Ti,Ca,Zr)O 2− x .
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Bayliss et al. (1989) studied this question.
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