68 BULLETIN 118, UNITED STATES NATIONAL MUSEUM. 



JADE. 



Varieties. — Jadeite and nephrite. 



Composition. — Jadeite, a mineral of the pyroxene group, is a 

 sodium aluminum silicate (NaAl(Si0 3 ) 2 ) with a granular to fibrous 

 but compact structure. Nephrite, a member of the amphibole 

 group, is a magnesium calcium silicate (Mg 3 CaSi 4 12 ) with a fibrous 

 structure. 



Crystallization . — Monoclinic. 



Color. — Gray or white when pure; often green, owing to the 

 presence of small amounts of iron silicates; usually mottled because 

 of irregular distribution of the coloring substance. 



Luster. — Vitreous ; translucent. 



Hardness. — 6.5 ; can not be scratched by a knife, and fairly durable. 



Specific gravity. — 3.35 ±0.10. 



Optical properties. — Mean refractive index for nephrite, 1.61; for 

 jadeite 1.67. 



Distinguished from imitations by its great hardness. True jade 

 is not produced artificially, but green glass made cloudy by stirring 

 in some pigment is sometimes used as an imitation. Not used as a 

 precious stone in the ordinary sense, but, because of its hardness and 

 toughness, has been much used, particularly by the Chinese, for 

 ornaments, carvings, etc. The hardness renders work upon it 

 difficult, and causes genuine jade articles to bring high prices. Igno- 

 rant buyers are often imposed upon by the substitution of a green 

 serpentine for the real article. Jadeite can usually be distinguished 

 from nephrite by its granular structure, nephrite being more dis- 

 tinctly fibrous. 



LIST OF SPECIMENS. 



JADE, variety JADEITE. 



CHINA. 



Carved buckle; bright green; 68 by 18 mm. Isaac Lea collection No. 1813 



Clasp of gold containing two pieces of green jadeite, 27 by 12 mm., at ends, 



and one of pink tourmaline, 42 by 25 mm., in center No. 1193 



Carved pendant; green to light green; 16.9 carats; 26 by 15 mm. Isaac 



Lea collection (fig. 9, pi. 12) No. 1814 



Carved pendant; green; 18.9 carats; 25 by 12 mm. Isaac Lea collection 



(fig. 11, pi. 12) No. 1815 



Two stones, irregular cabochon; bright green; 7.5 and 7.14 carats; 14 by 11 



mm No. 1191 



Charm; pale green and white; 31 by 24 mm. Isaac Lea collection No. 1816 



JADE, variety NEPHRITE. 

 CHINA. 



Disk with flower; gray-green; 5.5 cm. diameter. Gift of Clarence S. Bement. No. 1186 

 Reclining figure; light gray-green; 5.5 by 3.2 cm. Deposited by P. L. Jouy. No. 1189 



Disk with slit; gray-green; 5.5 cm. diameter No. 1187 



Carved ornament or buckle; gray-green; 10 by 2 cm No. 1188 



