378 



DESCRIPTIVE MINERALOGY. 



ORDER IV. ZIRCONIA. 



This order has only a single species, viz : 



1. Zirconiie, or Zircon. 



ZIRCONITE. 



Zircon. Ckavcland, PkiBips, Thomson, Bctuiant, Shcpanl and Dmm. 



midalcr Zircon. Mohs. 



Pyramidal Zircon. Jamcstm. — Pyra- 



Fig. 414. 



Description. Colour grey and liyacinlli-rcd ; also white, green, brown, and rarely yellow, 

 blue and red. It occurs regularly crystallized. Primary form an obtuse octahedron with a 

 square base. Fig. 414. P on P over the base, 84° 20' ; over a 

 pyramidal edge, 123° 15'. According to some authors, the pri- 

 mary is a right square prism. In some varieties, the cleavage is 

 very distinct. Fracture conchoidal. Lustre more or less adaman- 

 tine. Ranges from transparent to opaque. Brittle. Rather easily 

 frangible. Hardness 7.5. Specific gravity from 4.50 to 4.70. 

 Before the blowpipe, if pure, it loses its colour, but retains its 

 transparency, and does not fuse. It melts with borax into a trans- 

 parent glass. It is not acted on by acids. 



Varieties. Those varieties in which the cleavage is very distinct, and which have a hya- 

 cin'.h-red colour, are sometimes called Hyacinth ; while those which arc not thus characte- 

 rized, arc named Common Zircon, or Zirconitc. 



Composition. Conwwn Zircon. — Zirconia 69.00, silica 26.50, oxide of iron 0.50 {Kla- 

 pi'oth). 



Hyacinth. — Zirconia 70.00, silica 25.00, oxide of iron 0.50 [Klaprotli). 



Zircon from Ceylon. — Zirconia 64.50, silica 32.00, oxide of iron 2.00 {Vauquelin). 



Zircon from Expailly . — Zirconia 67.16, silica 33.48 {Berzcliiis). This mineral is a 

 silicate of zirconia, and its formula is Zr.OaSiOj. 



Geological Situation. In this State, zircon has heretofore been found only in primitive 

 rocks, either the granitic or limestone. I am not aware of its occurrence here in the trappean 

 formations. ; 



LOCALITIES. 



Essex County. At Hall's iron mine in the town of Moriah, about eight miles west of the 

 village of Port Henry, zircon has been found in a vein of white quartz, running through the 

 ore. The crystals are of a cinnamon-red colour, sometimes translucent, and often with the 



