TORBERNITE (or cupro-uranite), a hydrous uranium and copper phosphate, one of the "uranium micas." Crystals are tetragonal and have the form of square plates, often very thin. There is a perfect micaceous cleavage parallel to the basal plane, and on this face the lustre is pearly. The bright grass-green colour is characteristic. The hardness is 2.5 and specific gravity 3.5. The radio-activity of the mineral is greater than that of some specimens of pitchblende. It was first observed in 1772 at Johanngeorgenstadt in Saxony, but the best examples are from Gunnislake near Calstock and Redruth in Cornwall. The name torbernite is after Torbern Bergman : chal colite is a synonym. The crystals readily lose part of their water, passing over into "meta-torbernite" with changes in the optical characters. (L. J. S.) TORCELLO, an island of Venetia, Italy, in the lagoons, 6 m. to the N.W. of Venice. It was a flourishing city in the early middle ages, but now has 171 inhabitants and two interesting churches.
The former cathedral of S. Maria was founded in 645. The present building, a basilica with columns, dates from 864; the nave was restored in I oo8, in which year the now ruined octagonal baptistery was built. It contains large mosaics of the 12th century, strongly under Byzantine influence ; those on the west wall represent the Resurrection and Last Judgment. The seats for the priests are arranged round the semicircular apse, rising in steps with the bishop's throne in the centre—an arrangement unique in Italy. Close by is S. Fosca (ca. Ioi I), octagonal outside, with colonnades on five sides and a rectangular interior intended for a dome which was never executed, beyond which is a three-apsed choir.
See B. Schulz, Kirchenbauten auf dem lnsel Torcello (Berlin and Leipzig, 1927).