GIBRSITK. 131 



Persia, not far from Nichabour, and according to Agaphi 

 occurs in veins, that traverse the mountain in every direc- 

 tion. 



The callais of Pliny was probably turquois. Pliny, in 

 his description of it, mentions the fable that it was found in 

 Asia, projecting from the surface of inaccessible rocks, 

 whence it was obtained by means of slings. 



Uses. Turquois receives a fine polish and is highly es- 

 teemed as a gem. In Persia it is much admired, and the 

 Persian king is said to retain for himself, all the large and 

 more finely tinted specimens. The occidental or bone Tur- 

 quois, a much inferior and softer stone, is fossil teeth or 

 hones, colored with a little phosphate of iron. Green mala' 

 chite is sometimes substituted for turquois, but it is much soft- 

 er and has a different tint of color. The stone is so well 

 imitated by art as scarcely to be detected except by chemi- 

 cal tests. The imitation is much sofier than true turquois. 



gibbsite. — Hydrate of Alumina. 4iC(. 



In small stalactitic shapes or mammillary and incrusting. 

 Color grayish or greenish white ; surface smooth but nearly 

 dull. Structure sometimes nearly fibrous. Rarely in hex- 

 agonal crystals. H=3— 3-5. Gi— 2-3 — 2*4. 



Composition : alumina 65*6, water 34*4. — (Torrey.) Re- 

 cent examinations have shown that the mineral contains 

 phosphoric acid only in traces. Prof. B. Silliman, Jr., has 

 also found, in specimens examined by him, as impurity -a 

 proportion of silica without phosphoric acid. The mineral 

 has resulted from the decomposition of feldspar or some 

 aluminous mineral, and probably varies in composition. It 

 whitens but does not fuse before the blowpipe. 



Dif. Resembles chalcedony but is softer. 



Obs. Occurs in a bed of brown iron ore at Richmond, 

 Mass., and at Unionvale, Dutchess county, N. Y. This 

 species was named in honor of Col. George Gibbs. 



Lazulite. In compact masses ; rarely in oblique crystals. Color 

 fine azure blue, and nearly opaque, with a vitreous luster. H=5 — 6. 

 Gr=3057. Brittle. Contains phosphoric acid 41-8, alumina 35*7 

 magnesia 9-3, silica 21, protoxyd of iron 26, water 61=977. It in* 



What is said of its use? How is it distinguished from false or arti- 

 ficial turquois? What is the appearance of Gibbsite ? What is said 

 of its composition ? How is it distinguished from chalcedony ? What 

 is the constitution of lazulite? its color ? 



