LAUMONTITE, called also LAUMONITE, and by Werner, efflorescing zeolite, because it crumbles easily after exposure to the air. It is one of the hydrous silicates, having the following average composition, which is from an analysis by Dufrenoy of a specimen from Plupsburg, Me.: silica, 51.98; alumina, 21.12; lime, 11.71; water, 15.5=99.86. It crystallizes in oblique rhomboidal prisms and in lamellar masses. Hardness, 3.5 to 4; sp. gr. 2.29 to 2.36. Vitreous, inclining to pearly upon the faces of cleavage. Color white, passing into yellowish gray, sometimes red; transparent, translucent. becoming opaque, and Averdlent on exposure. Before the blowpipe it fuses into a frothy mass. With borax it fuses into a transparent globule. It is gelatinous when treated with nitric or muriatic acid, but is not affected by sulphuric acid without beat. It is found in cavities in amygdaloid, porphyry, syenite, trap, gneiss, and sometimes in veins in clay slate. It
was fhst found by Laumont in 1785 in lead-mines in Huelgoet, Brittany. Its principal localities are the Faroe islands, Greenland, Bohemia, Switzerland, flartileld moss in Renfrewshire; amygdaloid rocks in Kilpatrick hills, near Glasgow ; trap-rocks of Hebrides and north of Ireland; Peter's point. Nova Scotia, fine specimens associated with apophyl lite and other hydrous silicates; Phipsburg, Me.; Charlestown quarries, Mass., in gneiss. It is abundant in the trap copper veins on lake Superior, and on the n. shore of lake Superior, between Pigeon hay and Fond du Lac; at Bergen hill, N. J., in greenstone with datholite and apophyllite; and at Columbia bridge near Philadelphia. The change which it ordinarily undergoes on exposure to the air may be prevented by dipping it in a thin solution of gum arable which prevents the about 2 per cent loss of water.