Original paper

The crystal-chemistry of high-aluminium titanites

Oberti, Roberta; Smith, David C.; Rossi, Giuseppe; Caucia, Franca

European Journal of Mineralogy Volume 3 Number 5 (1991), p. 777 - 792

47 references

published: Oct 2, 1991
manuscript accepted: Apr 25, 1991
manuscript received: Oct 5, 1990

DOI: 10.1127/ejm/3/5/0777

BibTeX file

ArtNo. ESP147050305014, Price: 29.00 €

Download preview PDF Buy as PDF


Abstract A crystal-chemical study of "high-aluminium titanites", where XA1 = AL/(AL + Ti + Fe3+) ≥ 0.25, has been made using single-crystal X-ray diffractometry on four samples from three different rock-types and localities. The first refinement of a natural pure CaTiOSiO4 titanite in the F21/a space group is also presented. All of the high-aluminium titanites studied have Alia space group symmetry with linear trends between geometrical and chemical parameters. Increasing Al content provokes a strong contraction of the octahedral site geometry: as XA, approaches 0.50, the mean distance in titanites reaches that of the chemical end-member vuagnatite, in which the octahedral chains are not corner-sharing but edge-sharing. The distance decreases linearly with , but the SiO4 tetrahedra remain constant in size. The contraction of the octahedron does not explain by itself the apparent structural limit to Al substitution at around XAl = 0.50 previously suggested from experimental studies and natural observations ; this limit, if it is real, is probably related to problems with local charge balancing and/or with structural matching