274 E. K Willia 



- Crystals of Tourmaline with Orthoclase. 



found that the minerals came from a quarry worked by Messrs. 

 Koe and VVitherbee, five miles west of the town, and about 1500 

 feet above the lake. 



The tourmaline which presented the peculiarity was mainly 

 in the reddish feldspar, that in the white variety being, as a 

 rule, solid. The tourmaline occurs in long prisms with rarely 

 more than one termination. The observed faces are: Ehombo- 

 hedral, I, 1{R), —^', scalenohedral, — ^S" prisms, I, i-2, i-f. 

 The common form is shown in Fig. 1. The crystals are com- 

 monly distorted, and are frequently terminated by but a single 

 rhombohedral plane. Specific gravity, 8'11. Fuses before the 

 blowpipe easily, with intumescence, to a dark bead. 



In the specimens obtained, there seem to be two varieties of 

 combination of the feldspar with the tourmaline: in the first, 

 the tourmaline has imposed its form upon the feldspar; in the 

 second, each has influenced the other. 



1. There are two types of the first variety. 



Fig. 1 shows the tourmaline with a solid 

 termination, and the enclosed feldspar 

 pierced with small tourmaline prisms 

 which descend from the solid end with 

 their vertical axes parallel to that of the 

 1*^ enclosing shell. These shafts, as well as 

 the shell, decrease in thickness as they 

 recede from the head. The tourmaline 

 I ^ has thus a pyramidal cavity filled with 

 I*— feldspar ; and in one instance this cavity 

 is terminated by a face of - 1. The shell 

 is absent in places, with the feldspar 

 apparently crystallized according to the 

 prismatic' planes of the tourmaline. In 

 figure 1, the dark and light parts repre- 

 sent tourmaline and feldspar respectively ; 



^W 



figs. la. 16, Ic are sections of the same crvstal (fig. 1) parallel to 

 the basal plane of the tourmaline, and taken at the points indi- 

 cated by the letters a, b, c ; they show the gradual disappearance 

 downward of the tourmaline. 



