Characterisation of an unusual efflorescence salt on Egyptian limestone relief

Fibrous crystals, up to 2 cm long and 3 μm in diameter, have been observed on an Egyptian limestone relief, stored in a wooden cabinet at the Burrell Collection, Glasgow. X-ray diffraction and infrared spectroscopy have shown that the crystals are identical to an uncharacterised efflorescence first reported in 1971. Ion chromatography was used in conjunction with scanning electron microscopy, x-ray spectrometry, and thermogravimetry to determine the composition of the salt efflorescence. The salt comprises, primarily, calcium, acetate, chloride and nitrate ions. Proton nuclear magnetic resonance spectrometry at 400 MHz was used to establish the degree of hydration. The stoichiometric formula derived from the analyses is Ca3(CH3COO)3Cl(NO3)2· 7H2O. This is a new crystalline salt not previously characterised.