Fig. 1. Samples of Madagascar agates

Fig. 2. A map of Madagascar
Mahajanga and Antsohihy are labelled by quadrangular star and pentagram respectively

Fig. 3. Concentric circular strips observed at site 1 of MN-1 sample
(a): Under plane polarized light;(b): Under crossed polarized light

Fig. 4. (a), (b) are images of MN-1 at 100× magnification; (c), (d) are images of MN-1 at 200× magnification; (e) distribution of some quartz species at the site coloured by red and white of sample MN-1
(a), (c): Under plane polarized light;(b), (d): Under crossed polarized light

Fig. 5. (a) Infrared spectra of sample MN-1 (the red stripe, the white stripe, the brown area); (b) Infrared spectra of sample MN-3 (the brownish yellow parallel stripe, the white parallel stripe, the yellow area)

Fig. 6. Raman spectra of the white stripes in MN-1, MN-2 and MN-3

Fig. 7. (a) Raman spectra of colored stripes in MN-1, MN-2 and MN-3 and red spots in MN-4; (b) Raman spectra of colored areas in MN-1—MN-5

Fig. 8. The Raman spectra of an inclusion in MN-3 (a); the Raman spectra of the yellow inclusion in MN-5 (b)

Fig. 9. The genetic mechanism of agates from Madagascar