280 UNIVEHSITY OF VIRGINIA PUBLICATIONS 



mannite (michaelsonite, 5.44 per cent ZrO-2) contains 3.47 per cent Zr02; 

 and sipylite, a niobate of the rare earths contains 2.09 per cent of Zr02. 

 Zirconia is found in the titanosiUcates in the following amounts : Astrophyl- 

 lite, 1.0 to 5.0 per cent; johnstrupite, 2.84 per cent; mosandrite, 7.43 per 

 cent; annerodite, 1.97 per cent. A uraninite from Colorado gave 7.59 

 per cent Zr02;* and sometimes a trace is found in xenotime.f Most of the 

 minerals named are rare and occur in nepheline syenites of Norwaj' chiefly, 

 and in less quantity' in those of Greenland and Finland. 



Zircun.X 



Of the numerous zircon-bearing minerals enumerated above zircon is 

 the most widely distributed and occurs in greatest quantity. Baddeleyite, 

 the native oxide (Zr02) found in Montana, § Sweden, Cejdon, and Brazil, is 

 reported to occur in quantity at Sao Paulo, Brazil, and since it is already in 

 the form of the oxide it will probably prove more desirable for most pur- 

 poses than zircon. 



Zircon, an orthosilicate of zirconium, corresponds to the formula 

 ZrSi04 and when pure is composed of 67.2 per cent of zirconia (Zr02) and 

 32.8 per cent silica (Si02). Iron is frequently present in small quantity. 

 Zircon crystallizes in the tetragonal system, commonly in square prisms, 

 often elongated, ■n-ith pyramidal terminations. 1[ The crj^stals sometimes 

 form geniculated t'n'ins like those of rutile and cassiterite. The mineral 

 also occurs in formless grains. 



Zircon has a hardness of 7.5 and a density of 4.7. It is brittle, has 

 imperfect cleavage, conchoidal fracture, and adamantine luster. It is com- 

 monly opaque, and usualh^ some shade of browii, but sometimes colorless, 

 clear yellow, gray, green, red, etc. Molecular weight 183; molecular vol- 

 ume 38.7. It is infusible and insoluble in acids except when acted on in 

 powder with concentrated sulphuric acid. 



Two principal varieties of the mineral are usually recognized: (a) 

 ordinary, and (b) gem or hyacinth. The first of these is the commoner and 



* Hillebrand, W. F., On the Occurrence of Nitrogen in Uraninite and on the 

 Composition of Uraninite in General, Bull. 78, U. S. Geol. Survey, 1891, p. 65. 



t Iddings, J. P., Op. cit., p. 60. 



t Compiled from various authorities. 



§ Rogers, A. F., Baddeleyite from Montana, Amer. Jour. Sci., 4th ser., vol. 33, 

 January, 1912, pp. 54-56. 



If The crystallography of the mineral is simple and numerous studies have been 

 made by mineralogists of zircon crystals in a variety of associations and occurrences 

 from localities in this and foreign countries. 



