Newcomb Tourmalines. 9 



, Muscovite occurs of a clear, yellowish-green color in the direction 

 of the a. axis, but reddish-brown in the direction of c, and viewed 

 through a., it is transparent ; through c, feebly translucent in thick 

 crystals. The largest crystals are no more than two cm. by one or 

 one and a half. The general hexagonal form of the crystal is easily 

 distinguished, though perfect faces are rare. 



The albite occurs in druses generally, though some crystals are 

 from one to three mm. long, and these druses are glassy and per- 

 fectly transparent. The mineral occurs coating the surfaces of all 

 the other minerals, and sometimes filling seams of broken crystals. 

 Fragments of large, translucent crystals are found measuring more 

 than five cm. in diameter. These fragments often have a beautiful, 

 pearly lustre and a soft opalescence. Very handsome stones have 

 been cut from some of these fragments. 



Graphite occurs much in the same form as in the surrounding 

 limestones, though apparently not quite as abundant. 



Dipyre crystals occur from minute drusy, to large crystals, five 

 to ten cm. in length. All are glassy, translucent to transparent, and 

 in color, vary from a grayish-green to apple green. Large crystal- 

 line masses occur, enclosing crystals of sphene, penetrating quartz 

 and tourmaline, and the surface of the masses, as it reaches into the 

 enclosing calcite, is covered with glassy, drusy crystals, though 

 some are of considerable size. The dipyre crystals also have the 

 pitted appearance, as though incipient fusion had taken place, or 

 solution had begun to remove part of the mass. The large crystals 

 enclose in globular cavities masses of perfectly crystallized calcite. 



Many crystals have long, dark, acicular enclosures, which are ar- 

 ranged parallel to the vertical axis with great regularity. These 

 acicular crystals vary from one to fifteen mm. . or more in length. 

 Some are barely visible to the naked eye, while others, show a 

 splendent metallic lustre when properly turned. Some crystals are 

 apparently free from these enclosures, but the microscope reveals 

 them in great numbers. In general, under the objective they are too 

 minute to give any intimation as to their form. They are usually 

 nearly or quite opaque. What little light is transmitted appears of a 

 reddish brown. 



Rosenbusch, in his " Mikroskopische Physiographic," second edi- 

 tion, page 318, describes minerals of the scapolite group occurring 

 under similar conditions and containing similar inclusions, but in 

 the granular limestones, the crystals are quite regular and free from 



