A variety of shale or clay slate, containing iron pyrites, the decomposition of which leads to the formation of alum, which often effloresces on the rock.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). alum shale. Retrieved September 22, 2026, from http://smartdefine.org/alum_shale/definitions/1972830 |
| Chicago | Webster's. 2011. "alum shale" http://smartdefine.org/alum_shale/definitions/1972830 (accessed September 22, 2026). |
| Harvard | Webster's 2011, alum shale, Smart Define, viewed 22 September, 2026, <http://smartdefine.org/alum_shale/definitions/1972830>. |
| MLA | Webster's. "alum shale" 27 May 2011. Web. 22 September 2026. <http://smartdefine.org/alum_shale/definitions/1972830> |