Sulphate of Iron and Argilla
Sulphate of Iron is the common produce of the decomposition of rocks containing Iron Pyrites, and probably often contains Sulphate of Argilla; in which case it seems sometimes to have been taken for native Alum, although it wants the Alcali. The specimen before us is from Bacherstolln, in Schmölniz: it contains a considerable quantity of Argilla, but apparently no Alum; which is, however, readily produced from it, by adding a little Potash. Its sourer taste distinguishes it from pure Sulphate of Iron: it is also less astringent, and less liable to be acted upon by the atmosphere.
The specimen was lent me by H. Heüland, Esq. whose uncommon liberality deserves my warmest thanks.