CATALOGUE OF GEMS AND PRECIOUS STONES. 



71 



The mineral dissolves with effervescence in hydrochloric acid, 

 yielding a yellow solution which together with its color is sufficient 

 in most cases for identification. Occurs like azurite in weathered 

 copper ores, and is used for ornaments, especially table tops, etc., 

 and was formerly valued very highly. As a rule, sound pieces of 

 only moderate size are obtainable, and on the larger objects of art 

 small pieces are very skillfully utilized as a thin veneer. Azurite 

 is associated with malachite in the specimen figured below (fig. 7). 



LIST OF SPECIMENS. 

 SIBERIA. 



Cabochon, circular girdle; 



banded green and 



brown; 70.8 carats; 34 



by 6 mm. Isaac Lea 



collection (fig. 3, pi. 7). No. 1250 

 Tabular, elliptical girdle; 



banded dark and light 



green; G3.7 carats; 40 



by 32 by 4 mm No. 1248 



Tabular, circular girdle; 



dark green with light- 

 green concentric rings; 



49.79 carats; 31 by 4 mm. No. 1249 

 Cabochon, elliptical gir- 

 dle; dark and light 



green, banded; 42.67 



carats; 33 by 26 by 5 mm. No. 1251 



Microcline. — See under Feldspar, variety Amazonstone. 

 MOLDAVITE: TEKTITE. 



Synonyms and varietal names. — Local names dependent upon 

 sources are common, as Australites, billitonites, and obsidian bombs. 

 Suess proposes the general name tektite for the entire group. 



Composition. — Glass high in silica, alumina, and the alkalies. 



Crystallization.— None ; amorphous. 



Color. — Green to black. 



Luster. — Vi treous . 



Hardness. — 6 to 7. 



Specific gravity. — 2.31 to 2.5. 



Optical properties. — Refractive index variable, mostly low; op- 

 tically isotropic. 



Resembles in many cases ordinary green bottle glass. Its lower 

 index of refraction distinguishes it from any natural crystalline min- 

 eral. Found loose on surface or in gravels in various parts of Austra- 

 lia, Bohemia, and Moravia, and thought by some to be of artificial, 

 and by others of meteoric origin. The green variety, moldavite, has 

 sometimes been cut as a gem stone, but is of value only as a curiosity. 



-Malachite and azurite. 



