| Clue | Source | Date |
|---|---|---|
| Converted to or hardened like bone (8) | ||
| Turned to bone | The Times Concise | 11 Jun 2022 |
| Fossilised, petrified | Irish Times Simplex | 18 Feb 2022 |
| Fossilised, petrified | Irish Times Simplex | 13 Aug 2021 |
| Fossilised, petrified | Irish Times Simplex | 08 Apr 2021 |
| Turned to bone | Eugene Sheffer | 31 Oct 2020 |
| Turned to bone with age | Irish Times Simplex | 19 Jun 2020 |
| Turned into bone | Irish Times Simplex | 30 Nov 2018 |
| Turned to bone | Irish Times Simplex | 23 Aug 2018 |
| Changed into bone | ||
| Hardened into bone | ||
| Ultraconservative | ||
| Hardened | ||
| Fixed rigidly in a custom. |