CATALOGUE OF GEMS AND PRECIOUS STONES. 97 



Luster. — -Vitreous ; translucent. 



Hardness. — 5; not durable. 



Specific gravity. — 4.40 ± 0.05. 



Optical properties. — Mean refractive index, 1.7; double refraction 

 pery strong, 0.2; optically uniaxial, negative. 



The mineral dissolves with effervescence in hydrochloric acid, as 

 does calcite and several other carbonates, from which it can be dis- 

 tinguished only by reacting for zinc. It is found as a secondary 

 product associated with sulphide zinc ores above the permanent 

 water level. Bright colored specimens are sometimes cut cabochon 

 and used for scarfpins, etc. The value, however, is little greater 

 than the cost of cutting. 



LIST OF SPECIMENS. 



GREECE (LARIUM). 



Cabochon, elliptical girdle; pale green; 79.73 carats; 25 by 22 by 13 mm No. 595 



UNITED STATES. 



Arkansas. 

 Marion County: 



Cabochon, elliptical girdle; pale yellow; two gems, 49.26 and 11.04 carats; 

 26 by 22 by Sand 18 by 12 by 5 mm No. 594 



SODALITE. 



Composition. — Sodium aluminum chloro-orthosilicate, Na 4 Al 3 



Cl(Si0 4 ) 3 . m 



Crystallization. — Isometric. 



Color. — Intense blue. 



Luster. — Vitreous; translucent. 



Hardness. — 5.5; not durable. 



Specific gravity. — 2.20 ±0.05. 



Optical properties. — Refractive index, 1.48; optically isotropic. 



The mineral may be distinguished from lazurite, the mineral with 

 which it is most likely to be confounded, by failure to evolve hydro- 

 gen sulphide when treated with acids. It is occasionally cut cabo- 

 chon, but not widely used and of no great value. B}- artificial light 

 nearly black in color. 



LIST OF SPECIMEN'S. 

 UNITED STATES. 



Maine. 

 Litchfield, Kennebec County: 



Cabochon, elliptical girdle; deep blue; 4.44 carats; 14 by 12 by 5 mm. . No. 367 



Spessartite. — See under Garnet. 



SPHALERITE. 



Synonym . — Zinc-blende. 



Composition. — Zinc sulphide, ZnS, with some iron replacing zinc, 

 to which the color is probably due. 



