ZIRCON, the native zirconium silicate. ZrSiO.. Its crystals are tetragonal and [40070I pbous with thorite, xenotime, cassiierize and ruble. Though its crystal forms are very varied, they are usually prisms terminated by pyramids, the base being rare. Small crystals frequanly show a wealth of faces, among which the tziroonoids; or ditetragonal pyramids are prominent. It is a heavy mineral. its speak gravity averaging about 4.7, and it has a char acteristic greasy-adamantine lustre. Though often nearly or quite opaque, transparent crys tals are not uncommon, and owing to its hard ness, 7.5, strong double refraction and the variety of rich colon in which it is found. arras has long been prized as a gem. Its dispersive power is excelled only by the diamond. •Hya or 'jacinth' includes reddish, orange or brownish gem stones, while 'jargon' embraces the colorless, yellowish, grayish or smoky varie ties. It is often an important accessory con stituent of gneiss, syenite and many crystalline rocks. Because of its resistance to weatherinc
and abrasion it frequently occurs in fine link crystals in alluvial sands as in Ceylon, Brazil and the monazite region of North The finest zircon gems come from Ceylon and New South Wales, while France yields very small stones of remarkably fine red color. Ex cellent translucent to opaque crystals occur in Norway, the Ural Mountains, (ands (up to 15 pounds), in New York, New Jersey, Colo rado and North Carolina. By far the most important locality is in Henderson County, N. C., where many tons of crystals occur loose in the soil. Zirconia, derived from thus source, was used in the gWelsbach• or •Aner' mantles, but its incandescence had not sufficient permanency and its use has been superseded tT thoria. Zirconia is still useful as a refractors material in furnace and crucible linings, and because of its incandescence in the •Itier.- light,' which is an improvement on the oretinare time light.