Abstract
The vast majority of occurrence of baddeleyite, zirconolite, and calzirtite reported in the literature are in carbonatite in these coexist, and it is known to usually make a zirconolite metamict (e.g. Williams and Giere', 1996; Giere' et al., 1998; Bellatreccia et al., 1999). The accommodation ability of zirconolite for actinid element is applied to the disposal of nuclear waste (e.g. Malmstro"m, 2000). These Zirconium minerals are stable in SiO2-undersaturated environment on the observation of natural and synthetic sample (e.g. Vlasov, 1966; Malmstro"m, 2000). In Japan few occurrence of SiO2-undersaturated environment such as carbonatite cause extremely rare the occurrence of these Zirconium minerals, therfore the study of the natural specimens have not been done enough. In Japan little amount of baddeleyite and zirconolite has found in dolomite from Neichi mine, Iwate Prefecture (Kato and Matsubara, 1991), and little amount of baddeleyite and calziritite has found in contaminated rocks from Fuka mine, Okayama prefecture (Henmi et al., 1996). In this study, we confirmed the occurrence and coexistence of baddeleyite, zirconolite, and calzirtite from Ko-Oge island, baddeleyite and zirconolite from Yuge island, zirconolite from Myojin and Mutsuki islands, and Shinkiura mine, and baddeleyite from Kuwao in Al-Fe-Ti rich rocks. Zirconolite and calzirtite have stoichiometries close to CaZrTi2O7 and Ca2Zr5Ti2O16 respectively with different crystal structures. A natural zirconolite is the metamict or non-metamict mineral with undetermind polytype, zirconolite-2M is the two layered monoclinic polytype, zirconolite-3O is the three layered orthohombic polytype, zirconolite-3T is the three layered trigonal polytype of CaZrTi2O7, zirkelite is the cubic mineral with (Ti, Ca, Zr)O2-X, and polymignite is metamict zirconolite(Bayliss et al., 1989). Although the mineral neme calzirtite had been the mineral with stoichiometry close to Ca2Zr5Ti2O16 with tetragonal symmetry (e.g. Rossell, 1982; Sinclair et al., 1986), the usage of the name is improper after the structure of orthormobic has reported by Callegari et al. (1997).Occurrence: Baddeleyite from Yuge and Ko-Oge islands is too fine scale to observe with microscope, but it shows anhedron and is exclusively accompanied to ilmenite with BSE images. Zirconolite from Ko-Oge island shows anhedron with 100um of the maximum, is associated with ilmenite, pervskite, and anatase, and often is intergrow with calzirtite in Ca-added zone. Zirconolite is also occure as anhedron with a maximam 50um from Yuge, Myojin, and Mutsuki islands and exclusively accompanied with ilmenite and titanite. Calzirtite occur as anhedron inclusion with 2-20um of zirconolite in a lot cases and as anhedron individual crystal with 30um of maximum in rare cases, which is closely associated with perovskite in latter cases. A small amount of Ce phosphate mineral with no mineral that relates closely is also confirmed in Aluninum-Titanium-Iron rich rocks of Ko-Oge island. From Kuwao, we confirmed badeleyite and zircon accompanied to anatase in Al-Fe-Ti rich rocks. From Shinkiura mine, Al-Fe-Ti rich rocks correspond to emery that discovered first in Japan (Yoshimura et al., 1962). Confirmed Zirconium mineral in Shinkiura mine emery is a few grain size anhedron zirconolite associated with ilmenite in many cases.
