Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 27… (1911)
“ Unlike quartz, it is soluble in a boiling solution of sodium carbonate. Tridymite occurs in the cavities of acid volcanic rocks (rhyolite, trachyte and andesite) ; the best-known localities are Cerro San Cristobal near Pachuca in Mexico, the Euganean Hills near Padua, and the Siebengebirge on the Rhine. Probably identical with tridymite is the form of silica known as asmanite, found in the meteorite which fell at Breitenbach in the Erzgebirge, Bohemia. ”
