182 



ALUMINA. 



borax fuses with difficulty. Gelatinizes in muriatic acid. From the 

 Fassa valley, Tyrol. 



Humboldtilite. Crystals as above. Cleavage basal, distinct. Colo! 

 brown or yellow; luster vitreous. H=5. Gr=2'9— 3*2. Composi- 

 tion, silica 440, alumina 11*2, lime 32*0, magnesia 6*1, protoxyd oi 

 iron 23, soda 4*3, potash 0*4. Gelatinizes with nitric acid. From 

 Vesuvius in lava. Somervillite and mellilitc are here included. 



PETALITE. 



In imperfectly cleavable masses, affording a prism of 142° 

 Color white or gray, or with pale reddish oi* greenish shades. 

 Luster vitreous to subpearly. Translucent. H=6 — 6*5. 

 Gr=24— 2-45. 



Composition : silica 77*9, alumina 17*7, lithia 3*1, soda 

 I 3. Phosphoresces when gently heated. Fuses with dif- 

 ficulty on the edges. Gives the reaction of lithia like spod. 

 umene. 



Dif. Its lithia reaction allies it to spodumene, but it dif- 

 fers from that mineral in luster, specific gravity, and greater 

 fusibility. 



Castor. Supposed to be petalite. Zygadite is another lithia min* 

 eral : it occurs in twins like albite. From, the Hartz. 



Violan is a dark violet-blue mineral, resembling glaucophane. 



Glaucophane occurs in cleavable masses of a dull bluish color, and 

 in thin prisms. Translucent. Gr=l*08. H=5 - 5. Fuses easily. Con- 

 tains silica 565, alumina 12*2, protoxyd of iron 10 9, protoxyd of man- 

 ganese 0*5, magnesia 8'0, lime 2 2, soda 9'3. From the Island of 

 Syra. 



Wichtine is a black mineral rectangularly cleavable in two direc- 

 tions. Contains silica 563, alumina 133, protoxyd of iron 13"0, per- 

 oxyd of iron 40, soda 35, lime 60, magnesia 30. From Wichty in 

 Finland. 



EPIDOTE. 



Monoclinic In righ f rhomboidal prisms more or less 

 modified, often with six or more sides. M : T— 115° 24'. 

 T : e=128° 19'; a : a=109° 

 27'; e : a=125M6' 



Cleavage parallel to M ; less 

 distinct parallel to T. — Also 

 I massive granular and of a co- 

 lumnar structure. 



£ 



M 



Describe petalite. What is the proportion of lithia in its constitution? 

 low does it differ from spodumene 1 Where does it occur 1 What ia 

 he form of epidote ? 



