Raman spectra of organic compounds kladnoite (C6H4(CO)2NH) and hoelite (C14H8O2)—Rare sublimation products crystallising on self-ignited coal heaps

As minerals, aromatic compounds occur very rarely in nature. Not more than 10 of such minerals are known and most of them were described in the coal deposits where they were formed as a result of coal bed fires or burning of coal waste heaps. Raman spectra of kladnoite C6H4(CO)2NH (natural phthalimide) and hoelite C14H8O2, (natural 9,10-anthraquinone) display complex features. Raman microspectroscopy help to detect these phases non-destructively directly in the frame of rare samples. Investigated minerals are transformation products formed from gaseous phase originating in natural pyrolytical process occurring in the frame of coal heaps and coal series outcrops. It is recommended to include Raman spectroscopic characteristics of similar materials in databases for exobiological studies.