| Abstract: | Abstract Small crystals of an optically uniaxial Ti-bearing calcium aluminosilicate were discovered in a mixer furnace slag consisting mostly of åkermanitic melilite. The crystals have the same unit cell as those observed for a phase crystallized from slowly-cooled melts used to simulate the formation of aluminous inclusions in meteorites. Moreover, compositions of synthetic and meteoritic occurrences of the phase are all very similar and can be expressed in terms of a binary solid solution between the end-members Ca3TiAl2Si3O14 and Ca3Ti(AlTi)(AlSi2)O14. Thus, crystallographic and crystallochemical information obtained from crystals in the mixer furnace slag can be used to constrain the origin of similar crystals found in meteoritic inclusions. We separated crystals from the mixer furnace slag by acid leaching; some were used for EPMA analysis, others were crushed for study by TEM methods or X-ray powder diffraction. Convergent beam electron diffraction shows that the crystals belong to the trigonal (rhombohedral) class and have point group symmetry 3m. X-ray powder diffraction gives the unit cell parameters a = 0.791 ± 0.009 nm, c = 0.492 ± 0.006 nm. The results suggest that the mineral has space group symmetry P3ml or P31m. |
