Sakurai’s Object revisited: new laboratory data for carbonates and melilites suggest the carrier of 6.9 μm excess absorption is a carbonate

We present new room-temperature 1100 - 1800 cm^{-1} spectra of melilite silicates and 600 2000 three randomly orientated fine-grained carbonates to determine the possible carrier(s) a 6.9~micron absorption feature observed in variety dense astronomical environments including young stellar objects molecular clouds. focus on low-mass post-AGB star Sakurai's Object which has been forming substantial quantities carbonaceous dust since an eruptive event 1990s. Large grains cannot be responsible for 6.9-micron because similarly-shaped laboratory spectrum was produced by very low (0.1 per cent mass) carbonate contamination not detected at other wavelengths. Due high band-strength carbonates, we conclude that carry feature. Replacement with models object improves fits 6 7-micron Spitzer without significantly altering conclusions Bowey's previous except there is no link between abundance meteorites. With magnesite (MgCO3), 25-micron-sized SiC increased 10 50 better constrained. The mass similar PAH dust. Existing experiments suggest are stable below 700~K, however it difficult ascertain applicability these more studies required.