118 BULLETIN 118, UNITED STATES NATIONAL MUSEUM. 



LIST OF SPECIMENS. 

 UNITED STATES. 



New Jersey. 



Franklin Furnace, Sussex County: 



Brilliant, circular girdle; deep yellow; 11.045 carats; 12 by 11 mm. 



Gift of Clarence S. Bement No. 1086 



Three small gems, brilliant, circular girdle; pale green-yellow; total 



weight, 0.79 carat; 5 by 3 and 3 by 2 mm No. 547 



ZIRCON. 



Variety . — Hyacinth . 



Composition. — Zirconium orthosilicate, Zr(Si0 4 ). 



Crystallization. — -Tetragonal, habit prismatic. 



Color. — Colorless when pure, but usually showing disperse colors, 

 especially pale green, yellow, or brown, owing to iron and perhaps 

 other constituents; rarely blue. 



Luster. — Adamantine ; transparent. 



Hardness. — 7.5; a very durable stone. 



Specific gravity. — Averaging about 4.7. 



Optical properties. — Mean refractive index 1.95; double refraction 

 strong, 0.06; optically uniaxial, positive. 



Some varieties of zircon yield with the microspectroscope a bril- 

 liant and characteristic absorption spectrum, due to the presence of 

 small amounts of uranium in the lower state of oxidation. This 

 spectrum consists of eight narrow bands, the strongest of which lies 

 in the orange, the others being somewhat uniformly distributed 

 through the whole spectrum. Specimens free from uranium, how- 

 ever, show no spectrum whatever, so that this is not a certain test 

 for the mineral. The high specific gravity and refractive index are 

 sufficiently characteristic for identification. In this last respect, 

 indeed, the zircon resembles diamond in luster and play of colors, or 

 "fire." It is cut facetted and rather widely used as a precious stone, 

 although its colors are, as a rule, not particularly attractive. 



LIST OP SPECIMENS. 



AUSTRALIA. 



Queensland. 

 Policeman Knob: 



Brilliant, circular girdle; pale green-blue; 2.55 carats; 7.5 by 5 mm. 



Isaac Lea collection No. 1809 



Brilliant, circular girdle; pale green-blue; 2.55 carats; 7.5 by 5 mm. 



Isaac Lea collection No. 1827 



Brilliant, circular girdle; pale green-blue; 2 carats; 7 by 5 mm. Isaac 



Lea collection No. 1828 



Brilliant, circular girdle; pale green-blue; 1.59 carats; 6.5 by 4 mm. 



Isaac Lea collection No. 1810 



Brilliant, circular girdle; pale green-blue; 1.49 carats; 6 by 5 mm. 



Isaac Lea collection No. 1829 



Brilliant, circular girdle; pale green-blue; 0.96 carat; 5 by 4 mm. 



Isaac Lea collection No. 1811 



