ZIRCONIFEROUS SANDSTONE NEAR ASHLAND, VIRGINIA 291 



the common rock-forming t^ilicate minerals. In pegmatites and the few 

 recorded occurrences in veins and contact metamorphic deposits the associa- 

 tion frequently' comprises minerals usually regarded as having been formed 

 bj' pneumatolysis, such as tourmaline, fluorite, cassiterite, riebeckite, etc. 

 In alluvial and water sorted sands, the heavy resistant minerals of a variety 

 of mineralogical form occur, such as hematite, ilmenite, magnetite, chro- 

 mite, rutile, cassiterite, monazite, xenotime, tourmaline, spinel, garnet, 

 staurolite, etc., and sometimes gold and platinum. 



The demand for zircon is now small but, with the probable increased 

 use of zirconia (Zr02), it will likely soon become greater. 



Bohm* sums up the knoAvn and probable uses for zirconium substanti- 

 ally as follows: 



Zirconia (Zr02) has been used in place of lime and magnesia as the incan- 

 descing material in the oxy-hydrogen blowpipe, and a very small quantity 

 of zirconium nitrate is used in making mantles for gas lights. Large 

 quantities of zirconia were once used in the Nernst lamps, a form of incan- 

 descent electric lamp in which a small stick of zirconia and yttria is used as 

 a glower, but its consumption is not now so large, owing to the competition 

 of metallic filament lamps. Zirconium carbide has been used in making 

 incandesceiit electric lamps, but this also has been superseded by metallic 

 filament lamps. The property of incandescence possessed by zirconia 

 has tempted arc-lamp manufacturers to use it in their electrodes, but 

 thus far it has not ■ been used successfully. Zirconia is an excellent 

 insulator for both" electricity and heat and when mixed with a conductor 

 can be used for electric heaters. In the Heraeus iridium furnace the iridium 

 may be protected by a glaze made from a zirconium salt in place of the tho- 

 rium or yttrium salts now used. Zirconia makes an excellent and very 

 refractory crucible, which is manufactured in many sizes by a German 

 firm. Its refractoriness makes zirconia a suitable lining for electric fur- 

 naces, and Bohm suggests that it might be used for saggers, but for the 

 ceramic trade it must be free from iron and cheap. He also suggests its 

 use for the walls of furnaces, for the making of molds to withstand high 

 temperatures, and for heat insulation. Owing to its inertness zirconia 

 is suitable for chemical ware, and many forms are manufactured from it. 

 The same property has led to its recommendation for certain medicinal 



* Bohm, C. R., Op. cit., pp. 1261-1262. 



