LABKADORITE. 179 



subtranslucent. Luster of principal cleavage face pearly- 

 other faces vitreous. H=6. Gr=s=2'fi9— 2'76. 



Composition: silica 53*1, alumina 30*1, lime 12*3, soda 

 4 T), water 0'5. Like feldspar before the blowpipe, but fuses 

 with a little less difficulty to a colorless glass. Entirely dis- 

 solved by muriatic acid. 



Dif. Differs from feldspar and albite in containing a 

 large percentage of lime, and it is farther distinguished by 

 dissolving in muriatic acid, and generally by its chatoyant 

 reflections. 



Obs. A constituent of some granites, and was originally 

 from Labrador. It is abundant in Essex county, N. Y., at 

 Moriah, Westport and Lewis. 



Uses. Labradorite receives a fine polish, and owing ( to 

 the chatoyant reflections of rich and delicate colors, the speci- 

 mens are often highly beautiful. It is sometimes used in 

 jewelry. 



Glaucolite. Considered by Frankenheim identical with Labradorite. 

 Color lavender-blue, passing into green. From near Lake Baikal in 

 Siberia. 



Oligoclase. A feldspar-like mineral, with a distinct cleavage, nearly 

 white color, of imperfectly vitreous to somewhat greasy luster. H=6. 

 Gr=2-58— 2-67. Composition, silica 63-5, alumina 23-1, lime 24, 

 potash 2*2, soda 94, magnesia - 8. Fuses with difficulty, and not at- 

 tacked by acids. Occurs at Stockholm in granite, and at Arendal, 

 Morway, and elsewhere, in granular limestone. Also found at Had- 

 dam, Ct., with iolite ; at Danbury, Ct. ; at Unionville, Penn. 



Couzeranite, another allied specks from the Pyrenees, ot a gray or 

 greenish gray color. Composition near that of Labradorite. 



Latrobite. Resembles some reddish scapolites, but occurs in oblique 

 rhomboidal prisms, like the feldspars, and has been referred to the 

 species anorthite. Occurs in crystals and also in cleavable masses. H 

 = 6. Gr=2-7 — 2 8. Composition, silica 41 '8, alumina 32-8, lime 9'8, 

 oxyd of manganese with magnesia 5 - 8, potash 6 - 6. water 2*0. Fuses 

 with some intumescence. From Labrador in granite. 



Amphodelite is united with the species anorthite. 



NEPHELINE. 



In hexagonal prisms. Also massive; some- / <pPZ>\ 

 times thin columnar. S£_v-" 



Color white, or gray, yellowish, greenish, bluish- 

 red. Luster vitreous or greasy. Transparent to 

 opaque. H=5'5— 6. Gi=2'4— 2-65. 



Varieties and Composition. Nepheline includes 



How does it differ from feldspar and albite 1 For what is it usedl 

 What is the form of crystals of nepheline ? Mention its colors and luster 



