UNISILICATES. 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. 
Jt 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 trapezohedron 
represented in the figure. Cleavage imper- 
fect. Usually in dull glassy crystals, of a 
erayish color; sometimes opaque-white, dis- 
seminated through lava. Translucent to 
epaques ~H.= 5526. G.=2:5.. Brittle: 
Composition. K,AlO, Si, = 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, 

