CATALOGUE OF GEMS AND PRECIOUS STONES. 79 



Indiana. 

 Wabash River: 



One white pearl, 12.5 grains. Isaac Lea collection No. 1840 



Seventeen pearls, various colors and shapes, total weight, 168 grains. 



Gift of B. F. Wheeler No. 1837 



White River: 



One white pearl, 17.8 grains. Isaac Lea collection No. 1839 



Tennessee. 

 Holston and Clinch Rivers: 



Thirty-two small pearls, various colors and shapes; total weight, 72 



grains. Isaac Lea collection No. 1499 



LOCALITY NOT RECORDED. 



Bracelet and earrings of small pearls Xo. 1496 



Fish carved from pearl No. 1513 



Comb carved from pearl No. 1514 



Four pearl cat's-eyes, cabochon, circular girdle; gray-brown with pearly 



internal luster; average diameter, 10 mm. Gift of Wirt Tassin No. 825 



Brooch of mother-of-pearl, carved in form of a feather No. 1507 



Brooch of mother-of-pearl, carved in form of a leaf, with red portion of shell 



to represent a bunch of grapes No. 1508 



Peridot. — See under Chrysolite. 

 Perthite. — See under Feldspar. 



PHENAC1TE. 



Composition. — Beryllium ortho-silicate, Be 2 Si0 4 . 



Crystallization. — Hexagonal (trigonal), rhombohedral. 



Color. — Colorless when pure; sometimes colored yellow by traces of 

 impurities. 



Luster. — Vitreous ; transparent. 



Hardness.— 7.5; very durable. 



Specific gravity. — 2.95 ±0.02. 



Optical properties. — Mean refractive index, 1.66; double refraction 

 moderate, 0.02 ; optically uniaxial, positive. 



The mineral is best identified by its optical properties. It occurs in 

 pegmatites and in veins, and is a rare mineral and not widely used 

 as a precious stone, although it approaches the diamond in brilliance, 

 especially in artificial light. The name, from 4>iva^, deceiver, is said 

 to have been applied on this account. 



LIST OF SPECIMEN'S. 



SIBERIA. 



Brilliant, rectangular girdle; colorless; 5.22 carats; 12.5 by 11 by 7 mm. 



Isaac Lea collection No. 830 



Brilliant, square girdle; colorless; 2.14 carats; 8 by 5 mm No. 831 



Plasma. — See under Chalcedony. 



Porphyry. — See under Miscellaneous on page 120. 



Prase. — See under Chalcedony. 



