What is alum?

Simon Stephens (geologist and local resident) is interviewed by Taroona High students Ollie Mackay and Emily Duncombe.
 
The 3km long Alum Cliffs are made of Permian mudstone, containing pyrite, which oxidises to produce alum, found in small crevices along the cliff-face. Alum is used for dyeing, tanning and in medicine.