What is slag in geology ?

Slag : definition

The "slags" are residues of melting or roasting, of metallic composition or with high metal contents. They are produced at the same time as the scoria (of silicate composition) in industrial furnaces, foundries, and in general in all metallurgical centers.

In the old exploitations, the slag and the scoria were stored with the poor ore. When these were deposited at the seaside, the action of sea salts frequently caused neoformation at their expense of mineralogical rarities, often chlorides and iodides, such as penfieldite (Pb2Cl3 (OH)) on the photo (© Gianfranco Ciccolini). The Greek Lavrion, which concealed the most important lead and silver mines of Ancient Greece, is rightly famous for its mineralogical neoformations on slag and scoria.