Tufa Quotes

What is called "sponge stone" or "Pompeian pumice" appears to have been reduced by burning from another kind of stone to the condition of the kind which we see. The kind of sponge-stone taken from this region is not produced everywhere else, but only about Aetna and among the hills of Mysia which the Greeks call the "Burnt District," and in other places of the same peculiar nature. ...it seems to be certain that moisture has been extracted from the tufa and earth, by the force of fire, just as it is from limestone in kilns. (Vitruvius)
The stone in quarries is found to be of different and unlike qualities. In some it is soft... in others it is medium... in still others it is hard as in lava quarries. There are also numerous other kinds: for instance, in Campania, red and black tufas; in Umbria, Picenum, and Venetia, white tufa which can be cut with a toothed saw like wood. View quote
Vitruvius