514 REPORT OF NATIONAL MUSEUM, 1900. 



from (Ji-r, twice, and ffBevog^ strong, alluding to its unequal hardness 

 and electrical properties in two different directions. 



The mineral occurs commonly in long-bladed triclinic cr3^stals and 

 in bladed to sul)librous masses. Hardness, 5 to 7, depending upon the 

 direction and crystal face upon which the test is made. Specific 

 gravity, 3.56 to 3.67. Luster, vitreous. The color is commonly pale 

 blue, often a deeper hue along the center of the blades, also white, 

 gray, green, and black; pleochroism strong in colored kinds. 



Kyanite occurs principally in gneiss and muscovite and paragonite 

 schist. 



One hundred parts contain: Silica, 37; alumina, 63. 



LABRADORITE. 



Labradorite is one of the feldspars occurring in triclinic crystals 

 and cleavable to granular masses. Its hardness is 6; specific gravity, 

 2.72; luster, vitreous, passing into pearly, translucent to subtranslu- 

 cent; color, gray, brown, or greenish, sometimes colorless and glassy. 

 Owing chiefly to a peculiarity in its intimate structure, labradorite, 

 especially of the cleavable kinds, often shows a magnificent pla}'^ of 

 colors, in which blue and green predominate, while yellow, red, peai'l 

 gi'ay, orange, puce, amber, and peach blossom hues are apparent, 

 together with a golden and copper schiller. The mineral takes a high 

 polish, and, because of its chatoyant reflections, is often very beautiful. 



Labradorite is an essential constituent of various rocks, especiallj- 

 the basic kinds, and is usually associated with some member of the 

 pyroxene or amphibole groups. Labradoritic massive rocks are most 

 common among the Archaean formations. It was brought first from 

 the coast of Labrador, hence the name. 



One hundred parts contain: Silica, 53.1; alumina, 30.1; lime, 12.3; 

 soda. 4.5. 



LAPIS-LAZULI. 



Lapis-lazuli, long thought to be a simple mineral, consists of a mix- 

 ture of a bluish substance (lazurite) with granular calcite, scapolite, 

 diopside, amphibole mica, p3a"ite, etc. The richly colored kinds are 

 highh^ esteemed for costly vases, mosaics, and other ornamental work. 

 Color, rich Berlin or azure blue, violet blue, and greenish blue; occa- 

 sionally containing a colorless substance and frequently including brass 

 yellow specks of pyrite; these are often so numerous as to produce a 

 spangled appearance. Its hardness is 5.5; specific gravity about 2.4; 

 luster, vitreous; translucent. 



Lapis-lazuli occurs commonly massive in limestone and in a granitic 

 rock. 



In composition it carries in 100 parts: Silica, 31.7; alumina, 26.9; 

 soda, 27.3; sulphur 16. 



