Perovskite alteration in kimberlites and carbonatites: the role of kassite, CaTi2O4(OH)2

Styles of Alteration of Ti Oxides of the Kimberlite Groundmass: Implications on the Petrogenesis and Classification of Kimberlites and Similar Rocks

“…A relatively low SiO 2 and high water activities were necessary to avoid the crystallization of titanite and to favour the crystallization of hydrogarnets. Slight replacement of perovskite by anatase in SK-1 could be indicative of a decrease of temperature under conditions of medium to high f (CO 2 ), following the thermodynamic calculations data [15]. However, the same experimental data suggest that the strong replacement of perovskite by kassite in SK-2 needs a high f (H 2 O) and a low activity in alkalis.…”

“…Kassite [CaTi2O4(OH)2] has a very similar chemical composition to cafetite (CaTi2O5•H2O). The identification of kassite from the SK-2 kimberlite was confirmed by comparing the kassite Raman spectrum with the available spectrum of kassite standards [15] (Figure 3b).…”

“…The microRaman study also confirmed the identification of the second generation of perovskite (type 2) by comparison with the spectrum of the magmatic perovskite (type 1) (Figure 3d). Minor The identification of kassite from the SK-2 kimberlite was confirmed by comparing the kassite Raman spectrum with the available spectrum of kassite standards [15] (Figure 3b).…”

“…Identity of anatase was confirmed by microRaman spectroscopy and its spectrum was compared with that of submicroscopic anatase, mixed with calcite, altering perovskite in carbonatites [14,15] ( Figure 3a). Calcite has a peak at 1088 cm −1 which corresponds to the vibration of the CO 3 group [15]. However, calcite is absent from the products of alteration of the perovskite from Siddanpalli.…”

“…However, perovskite may be unstable in CO 2 -rich fluid environments characteristic of the final stage of some carbonatites and kimberlites worldwide [12][13][14]. Products of perovskite replacement in kimberlites may include kassite, anatase and titanite along with calcite, ilmenite and unidentified LREE-Ti oxides [13,15]. Similarly, carbonatitic perovskite is replaced by anatase with calcite and finally by ilmenite and ancylite [13].…”