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368 SILICATES. Adularia and the nearly opaque common felspar are found in plutonic and metamorphic rocks; the transparent varieties having a bright vitreous lustre, in imbedded crystals, having but tew faces, and traversed by numerous cracks, called glassy felspar or sanidine, in volcanic rocks. It has been observed that common felspar exposed to a high temperature in the inner wall of a furnace has acquired the appearance of glassy felspar. Adularia is found in St. Gotthardt, Mont Blanc, JJauphme, Arendal in Norway, in the granite of Arran, in veins ■ e 1'intagel in Cornwall, on Snowdon. A variety ex hibiting a play of colours was found in Ceylon, in the zircon syenite of the south of Norway, in Greenland. Common fel spar in attached crystals at Baveno on the Lago Maggiore, Lomnitz in Silesia, the Morne mountains in Ireland, Alabaschka near Mursmsk and several other places in the Ural, in imbedded crystals at Karlsbad and Elbogen in Bohemia, Ochsenkopf, Kos- sein and Kirchenlamitz in the Fichtelgebirge, Eglersburg in Thuringia, near Eio Janeiro in the Brazils. Green felspar (amazon-stone) is found on the east side of Lake Ilmen. Glassy felspar occurs in trachyte in the Drachenfela on the Ehme, Mont d’Or and other places in Auvergne, in Mexico, Chdo; at Oberbergen, Bischoffingen and Kothweil in Baden, in Hungary, the Euganean hills, Milo, Kamtschatka, Sitka, iu trachytic lava at Montamiata, Viterbo, Potzzuolo, Ischia in Italy, in Iceland; in the basaltic conglomerate of Dorenberg near Cassel; in volcanic masses about Vesuvius and the lake of Laach, in Eum, in pitch-stone in Arran. The murchisonite of Levy is a flesh-red variety of felspar (o = 2V>l) occurring in rolled pebbles at Heavitree near Exeter, which has, besides the usual cleavages c, b, at right angles to each other, a third cleavage a, such that cb = 90° o', ?c = 100° so', la = 9 0 17'. An opalescent play of light is observable on the cleavage planes a. Some of the crystals are twins, the twin-face being a. I he transparent colourless felspar from Ceylon (moon-stone) and the iridiscent felspar from Eriedrichswarn have the same cleavages and play of light. Crystals of flesh-red felspar having the faces b, m and probably either c, x or y, have been formed in a copper furnace in Mannsfeld; and crystals, perfectly re sembling the adularia from St. Gotthardt, having the faces b, c, in, and sometimes a and z, both single and in twins (twin-face c), were found by the younger Hausmann between 'five and six eet above the hearth of an iron furnace at Josenhshiitte near otoloerg. I elspar is liable to suffer decomposition, forming a silicate of sib aS f 8 °i U i V 1 wa * er > which is washed away, leaving a hydrous Ca °; . m * na (porcelain-clay or kaolin). It is sometimes ver e into a substance like steatite, or into a mechanical