PHYSIOGRAPHY. 299 



Labradorite. 



Cleavage parallel with P and M most distinct, that in the 

 direction of the remaining primary face very imperfect. 



Lustre, upon the cleavage planes of P pearly, passing in- 

 to vitreous. Color white, passing into grey, with a tinge of 

 blue. Opalescent and iridescent tints appear in directions 

 not coincident with the cleavages.* Translucent on the 

 edges. 



Brittle. Hardness =6-0. Sp. gr. =2-69 . . . 2-76. 



1. Before the blow-pipe, Labradorite resembles Feldspar. With ox 

 ide of nickel and borax, it affords a blue pearl. It is entirely dissolved 

 by heated muriatic acid. 



2. Analysis. 



By KLAPROTH. 



3, Labradorite occurs in sienitic rocks ; also as a regular constituent 

 in several kinds of gabbro rocks, with serpentine. 



4. It was first brought from the coast of Labrador. It occurs also in 

 Ingria, in large, but ill defined crystals, in Greenland, and as a constit- 

 uent of several rocks in various places of the Hartz, Saxony, near Flor- 

 ence, &c. The variety commonly quoted from Norway, in the zircon- 

 sienite of Friediichsvlirn, belongs to the species of Feldspar, and not to 

 Labradorite. 



Labradorite is but little known in the U. S. But one locality of any 

 importance is known to exist in the country, which is situated at the dis- 

 tance of 60 miles west of Mount Moriah, upon Lake Champlain, (N.Y.) 

 in an almost uninhabited country. It here exists in the greatest abun- 



* From the researches of Dr. BREWSTER, it appears that these tints 

 arise from the existence of empty crystallized cavities distributed through 

 the mass. 





