Fig. 1. Location of Chiapas, Mexico

Fig. 2. Location of Amber Mine, Simojovel Mexico (stars indicate main sites^[4])

Fig. 3. Polished red blue amber
(a): Part of red skin is remained; blue green and maroon appear on a piece of amber at the same time; (b): Red skin covers the whole amber

Fig. 4. Amber samples
MXG-1—MXG-8 are red blue ambers; MXG-9—MXG-12 are black skin ambers

Fig. 5. Fluorescence characteristic of red blue amber under natural light and long-wave UV (365 nm)
(a): MXG-7 and MXG-8 under natural light; (b): MXG-7 and MXG-8 under ultraviolet light

Fig. 6. Microscopic characteristics of carbide skin and red part of red blue amber
(a): Blood amber and carbonized skin; (b): Surface of carbonized skin; (c): Uneven thickness of red part; (d): Black dot-like inclusions gathered to form red part, the color transition is obvious from carbonized skin 1, to blood amber 2 and to gold amber 3

Fig. 7. Internal inclusions in red blue amber samples
(a): Disc-like inclusions; (b): Gas-liquid two-phase inclusion; (c): Black dot-like inclusions; (d): Plant debris inclusions; (e): Black organic inclusions; (f): Miscellaneous flocculent dark organic inclusions

Fig. 8. Internal inclusions in black leather amber samples
(a): Flow pattern; (b): Elongated impurity inclusion;(c): Impurity inclusions and disc cracks(under crossed polarized light)

Fig. 9. Infrared spectra of Mexican red blue amber samples

Fig. 10. Infrared spectra of internal red blue amber and black skin amber samples

Fig. 11. Internal and red part photoluminescence spectra of red blue amber samples

Fig. 12. Internal photoluminescence spectra of red blue amber and black skin amber samples
MXG-5 and MXG-6 are red blue ambers, MXG-9 and MXG-10 are black skin ambers

Table 1. Samples appearances and fluorescence characteristics

Table 2. Positions and assignments of infrared absorption peaks of samples