TJNISILICATES. 271 



Composition. Silica 45-5, alumina 31*8, soda 9*1, lime 

 3-5, iron 0*8, sulphuric acid 5-9, sulphur 0*9, chlorine 0*4, 

 water 0*1 — 98*0. B.B. fuses to a white translucent or 

 opaque glass, and if calcined and reduced to powder loses 

 its color in acids ; is decomposed with the evolution of 

 hydrogen sulphide, and the solution gelatinizes on evapora- 

 tion. "The color of the mineral is supposed to be due to 

 sodium sulphide. The mineral is not homogeneous, but the 

 exact nature of the ultramarine species at the basis of it is 

 not yet ascertained. 



Obs. Found in syenyte and granular limestone, and is 

 brought from Persia, China, Siberia, and Bucharia. The 

 specimens often contain scales of mica and disseminated 

 pyrites. 



* The richly - colored lapis - lazuli is highly esteemed for 

 costly vases, and for inlaid work in ornamental furniture. 

 It is also used in the manufacture of mosaics. When pow- 

 dered it constitutes a beautiful and durable blue paint, 

 called Ultramarine, which has been a costly color. The 

 discovery of a mode of making an artificial ultramarine, 

 quite equal to the native, has afforded a substitute at a com- 

 paratively cheap rate. This artificial ultramarine consists 

 of silica 45*6, alumina 23*3, soda 21*5, potash 1*7, lime 

 trace, sulphuric acid 3-8, sulphur 1 # 7, iron 1*1, and chlorine 

 a small quantity undetermined. It has taken the place in 

 the arts, entirely, of the native lapis-lazuli. 



Leucite. — Amphigene. 



Dimetric. Form very nearly that of the trapezobedron 

 represented in the figure. Cleavage imper- 

 fect. Usually in dull glassy crystals, of a 

 grayish color ; sometimes opaque-white, dis- 

 seminated through lava. Translucent to 

 opaque. H. =5*5-6. G. =2*5. Brittle. 



Composition. K.-, Al Ojo Si 4 = Silica 55-0, 

 alumina 23-5, potash 21-5 = 100. B.B. infu- 

 sible. Moistened with cobalt nitrate and ig- 

 nited assumes a blue color. Decomposed by hydrochloric 

 acid, without gelatinizing. 



Diff. Distinguished from analcite by its hardness and in- 

 fusibility. 



Obs. In volcanic rocks, and abundant in those of Italy, 



