| Composition | Center edge | ||
| Na2O | 0.05 | 0.03 | 0.05 |
| FeO | 30.49 | 31.83 | 31.92 |
| K2O | 0.03 | 0.02 | 0.03 |
| SiO2 | 37.54 | 37.32 | 37.17 |
| MnO | 0.77 | 0.93 | 1.16 |
| MgO | 2.05 | 2.30 | 2.09 |
| CaO | 7.61 | 5.43 | 5.38 |
| Al2O3 | 21.13 | 21.35 | 21.43 |
| Total | 99.71 | 99.19 | 99.28 |
| Na | 0.02 | 0.01 | 0.02 |
| Fe | 4.08 | 4.29 | 4.30 |
| K | 0.01 | 0.00 | 0.01 |
| Si | 6.01 | 6.01 | 5.99 |
| Mn | 0.10 | 0.13 | 0.16 |
| Mg | 0.49 | 0.55 | 0.50 |
| Ca | 1.31 | 0.94 | 0.93 |
| Al | 3.99 | 4.05 | 4.07 |
| Total | 16.02 | 15.97 | 16.02 |