Revisiting stantienite-like black materials: beyond the "black amber" label.

Black organic materials historically described as stantienite, pseudostantienite or "black amber" may encompass spectroscopically heterogeneous materials whose chemical identity cannot be inferred from macroscopic appearance or historical terminology alone. In this study, a set of stantienite-like black organic materials was examined using ATR-FTIR spectroscopy, and selected samples were additionally analyzed by SEM-EDS. The results were compared with those obtained for reference fossil and subfossil resins, jet, and petroleum asphalt. The spectra were evaluated qualitatively and using FTIR-derived indices describing the relative contributions of aliphatic, aromatic, carbonyl and oxygen-containing structural features. SEM-EDS observations provided additional qualitative information on surface composition and local heterogeneity. The investigated black materials differed clearly from the resin reference materials and showed variable combinations of aliphatic CH stretching bands (3000-2840 cm-1), carbonyl absorption (1800-1650 cm-1), aromatic CC vibrations (1660-1580 cm-1) and aromatic CH out-of-plane deformation bands (900-650 cm-1). The FTIR-derived indices indicated that the black materials (BM) were spectroscopically heterogeneous and displayed gradual variability that could be described by tentative BM-I, BM-II and BM-III subgroups. The results indicate that the term "black amber" should not be interpreted as evidence that stantienite-like materials are amber or fossil resins. These results support a reassessment of stantienite-like materials beyond the "black amber" label and indicate that they represent heterogeneous organic materials showing variable spectral relationships to resinous, carbonaceous, and bituminous reference groups.