| Layer | Composition (wt%) | Phase | |
| O | Fe |
| |
1 | 1 - 5 | 95 - 99 | Fe + (FeO) | |
2 | 14 - 20 | 80 - 86 | Fe + FeO + (Fe3O4) | |
3 | 23 - 30 | 70 - 77 | Fe2O3 + Fe3O4 + FeO |