Mineral
Alum shale
Picture to come.
A grey, crumbly shale found notably on the Yorkshire coast, from which alum can be extracted by roasting, steeping and boiling with other ingredients. There is no evidence that it was worked for alum in 12th-century England: the English alum-shale industry began around 1600 in Cleveland. In this period it would have been simply rock; all alum used in England was imported.
Caveats (confidence: high)
Included honestly: the game allows it to be gathered, but its use as an alum source in England is roughly four centuries later than the setting. No known 12th-century use.
Sources: en.wikipedia.org
Made by
- Quarry stone