Throughout much of the Piedmont Plateau and Mountain regions the decomposition of felspar and of other aluminous minerals has resulted in a deep soil of clay with which more or less sand is mixed.
His account of the aluminous district of Tolfa and adjacent hills, published in 1786, gained for him the notice of the king of Naples, who invited him to inspect the mines and similar works in that kingdom, and appointed him professor of mineralogy to the royal artillery.
Thus Strabo states that in his time a process was employed for refining and purifying gold in large quantities by cementing or burning it with an aluminous earth, which, by destroying the silver, left the gold in a state of purity.
Potassium bisulphate is useful in the preliminary treatment of refractory aluminous ores.
Alumina is high in the finer clays (18 to 30%), and they are the most aluminous of all sediments, except bauxite.