| Code | Definition | Number of Accessions |
| 1 | Extremely hard (very difficult to break, need hammer) (Bartre) | 16 |
| 2 | Hard (difficult to break, need hammer) (Desmaye, Largueta) | 20 |
| 5 | Intermediate (broken by hand with effort) (Texas) | 10 |
| 7 | Soft (broken by hand) (Princesse) | 9 |