CATALOGUE OF GEMS. 513 



is most commonly found in an altered condition or inclosed in altered 



iolite. 



One hundred parts contain: Silica, -±9.6; alumina, 33.8; magnesia, 

 8.7; oxide of iron, 7.9. 



ILVAITE. 



Ilvaito has little value as a gem. but is occasionalh^ used for the let- 

 ter I in sentimental jewelry. It is iron black in color; has a hardness 

 of 6; a specific gravity of 3.99,-and a submetallic luster. The mineral 

 crystallizes in the orthorhombic system, commonly in prisms, also 

 occurring columnar or compact massive. 



One hundred parts contain: Silica, 29.3; oxides of iron, 54.8: lime, 

 13.7; water, 2.2. 



ISOPYRE. 



Occurs in compact masses with cleavage. Its color is grayish or 

 velvet black to dark green, occasionally spotted red like heliotrope 

 and then used as a gem. Its hardness is 6 to 6.5; specific gravity, 

 2.912; luster, vitreous, and is translucent to opaque. Isopj-re occurs 

 in a quartzose granite near Penzance, Cornwall, England, and in a 

 breccia near Edinburgh, Scotland. 



The mineral contains in 100 parts: Silica, 47.09; alumma, 13.91; 

 iron, 20.07; lime, 15.43; copper, 1.94. 



JADE. 



Jade, as commonly used, is a generic term including various mineral 

 substances, as chloro-melanite or jadeite, nephrite, saussurite, pseudo- 

 nephrite, of tough, compact texture, and ranging in color from cream 

 white to dark green and nearly black. The Asiatic jade is usually 

 pale green or bluish white, while that of New Zealand is dark green. 



The term jade includes properly two minerals only — -nejjhrite and 

 jadeite. The one is a tough, compact, fine-grained tremolite, a variety 

 of amphibole, having a hardness of 6 to 6.5 and a specific gravity of 

 2.96 to 3.1. The other is a tough, fibrous foliated to closely compact 

 mineral grouped with the pyroxenes. Its hardness is 6.5 to 7 and its 

 specific gravity 3.33 to 3.35. 



The lack of brilliancy in jade makes it of little value as an article of 

 jewelry, but its great toughness renders it eminently suitable for 

 ornamental vases and other carved work displa34ng delicacy of 

 workmanship. 



KYANITE. 



Kyanite, when transparent and of a good color, is employed as a gem. 

 The name is from Kvavog^ blue, though the mineral affords examples 

 of other colors, such as white, gray, green, and black. Disthene is 



