Raman spectroscopic study of mellite--a naturally occurring aluminium benzenehexacarboxylate from lignite--Claystone series of the tertiary age.

Raman spectra have been obtained for crystals of the organic mineral mellite, from three different sites. Mellite occurs in the frame of the Tertiary series including lignite and coaly slates at Artern (Thuringia), Tula (Russia) and Bílina (Northern Bohemia). Mellite, Al(2)C(6)(COO)(6) x 16H(2)O, can be considered as evidence of previous biological activity in the geological record, similar to other salts of carboxylic acids such as whewellite and weddellite. Assignments of the major Raman features of mellite are proposed on the basis of comparison with the parent, mellitic acid, C(6)(COOH)(6). During diagenesis and epigenesis, mellite is formed from the reaction between organic carbon rich solutions with aluminosilicates, hence, with the current interest in the adoption of Raman spectroscopy for incorporation into robotic instrumentation for space mission landers, it is important that organic minerals be included into a spectroscopic database for the recognition of biomolecular signatures for remote life-detection experiments.