Laumonite (called by Werner efflorescing zeolite, from its property of crumbling at the touch after exposure to the air), a mineral found in cavities in amygdaloidal rocks, and also in syenite and porphyry; named after Laumont the mineralogist, who first observed it in 1785 in the lead mines in Brittany. It occurs in crystals of the form of oblique rhom-boidal prisms, and also in lamellar masses. The color is yellowish or grayish white; it is transparent, and has a vitreous lustre, but becomes opaque and usually pulverulent on exposure; hardness 3.5-4; specific gravity 2.3-2.4. In composition it is a hydrated silicate of alumina and lime, a specimen from Phippsburg, Me., giving the following proportions of its ingredients: silica 51.98, alumina 21.12, lime 11.71, and water 15.05=99.80. Some varieties are so liable to effloresce and fall to fine powder, that they can be preserved only by a coating of gum arabic, or by keeping them in moist air. The mineral is found principally in the Faroe islands, the Hebrides, Greenland, and Switzerland, but occurs also on the N. shore of Lake Superior, at Bergen Hill, N. J., and at Port George, Nova Scotia, where the veins are sometimes 3 in. thick.