Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/144

 132 one or two rocks in different countries, which almost always accompany serpentine.

It is not in Cornwall alone, that diallage is found in the immediate vicinity of serpentine. It is found on Mount Musinet, two leagues west of Turin, a mountain almost entirely composed of a hard greenish serpentine. The mineral named after Saussure, which he himself calls smaragdite, is the green variety of diallage united with jade. The semiopal or hydrophane is found in a subordinate bed in the same mountain. I am sorry to say that this last mineral becomes daily more rare: I was not able to procure on the spots single well characterised specimen, after employing several hours in searching for it.

I found on Monte Baldissero, in the Circle of Ivres, the metalloidal diallage, accompanied also with semiopal, nearly in the same geological position as on Mount Musinet; the only difference is, that the rock which forms the mass of the mountain approaches more to the nature of steatite than of serpentine. I also found in a vein on Monte Balrdissero a white earth in rounded mamillated masses, which used to be taken for pure alumine, but which Giobert has shewn to be magnesia. It is used in the manufacture of porcelain.