PRECIOUS STONES. 597
the New York World memorial presented to the eminent sculptor, Bartholdi, was made of it. Preparations have been made to polish this material at Sioux Falls, Dakota, water power and other facilities being found there, and during the present year (1887) important developments are expected in the form of table tops 2 feet across made from a single section.
Hydrophone. An opaque white hydroj^haue of great interest has been found in Colorado and the finder has named it " magic stone," because, as usual with this mineral, it possesses the property of becoming absolutely transparent if water is dropped slowly on it from one to three minutes. It is so porous that it will absorb its own weight of water; it quickly recovers its opacity. The linder suggests that the stone be used for seals, rings, and scarf pins, as by reason of its opacity it would completely conceal portraits, mottoes, or mementoes which could be brought to view when desired by the application of a little water. This is the finest hydrophane known.
Chalcedony. Near Cisco, Utah, a pink chalcedony has been found which admits of a high polish, but which has-not yet been introduced in any quantity.
Agate. The beautiful little agate pebbles from the Pescadero beach, in California, are sold in large quanties and in different forms, polished, and unpolished, and loose, or in vials of water. Occasionally some of them are found inclosing a pebble moving in liquid, like the hydrolites from Uruguay and the chalcedony from Tampa Bay, Florida. They vary in diameter from T\T to J, rarely 1 inch.
Obsidian. Mr. J. P. Iddings has contributed a paper to the Seventh Annual Eeportof the United States Geological Survey, describing the obsidian cliff in the Yellowstone Park, Wyoming, stating that it presents the partial section of a flow of obsidian ; the dense glass which forms the lower portion is from 75 to 100 feet thick. A remarkable feature about it is the development of prismatic columns which form its southern extremity, rising 50 or 60 feet, and being only 2 to 4 feet in diameter. The color of the material is for the most part jet black, but some of it is mottled and streaked with bright brownish red and various shades of brown (mountain mahogany), passing into dark or light yellow, purple, and yellowish green. The great quantity and beauty of the material invite attention to its use in the arts.
Azurite and Malachite. Mr. T. A. Heistand obtained masses of azurite, and malachite resulting from the alteration of azurite, which, being botryoidal in form and showing the two minerals in distinct layers, formed a most beautiful ornamental stone when cut across the tops of the mamillary masses (1 to 3 inches across) and carefully polished. There are from two to four alternate and concentric rings of each color, which produce a very novel and pleasing effect. If this were fouud in sufficieut quantity it would make a very valuable ornamental stone.
