434 NATURAL HISTORY. 



varying from one hundred to two hundred and forty 

 florins. 



V. Feldspath or Feldspar forms an exclusive fam- 

 ily. Luster vitreous, passing into pearly; translucent 

 on the edges ; sometimes colorless, at others white, gray, 

 flesh-colored; seldom yellow or greenish. Brittle; 

 fracture uneven, somewhat conchoidal. H. = 6, G. = 

 2.5 to 2.58. Represented first by 



The Common Feldspar, only moderately translu- 

 cent, is one of .the constituents of the granite, gneiss, 

 mica, slate, and, associated with porphyry, often occurs 

 in crystalline or solid masses in this primary rock form- 

 ation. Feldspar, decomposed and called Kaolin, is 

 an important adjunct in the making of porcelain or 

 China ware ; deprived of alkali and potash it is used like 

 gypsum to promote the fertility of fields. Moonstone is 

 an opalescent variety of Adttlana, is very hard, and, 

 when polished, presents peculiar pearly reflections. 



Labradorite Labrador Feldspar. Luster vitre- 

 ous, translucent, pearly on the edges. This stone, espe- 

 cially on cleavage, presents the most beautiful series of 

 colors from internal reflections, as blue, red, yellow, and 

 green. H. = 6.0, G. = 2.68 to 2.72. Occurs in 

 Finland and North America. Originally from Labra- 

 dor, is abundant in New York. Receives a fine polish, 

 and is used for making jewelry, boxes, buttons, va- 

 ses, etc. 



VI.' Pitch Stone Family, to which belong, first, 



Pitch Stone, which has the luster of pitch rather 

 than glass; translucent on the corners or edges. Color 

 green, yellow, red, brown, gray, black : often waved or 

 clouded. Fracture flat, conchoidal, splintery. Found 

 in large, rock-like masses ; it forms whole mountains in 



