INTRODUCTION TO THE ROCKS. 39 



Thus, in several particulars, this mineral differs from quartz. 

 Its name is Feldspar. But feldspar is not always white nor 

 cream -colored. Very often it is pink-tinted ; often almost red. 

 But you may know it to be feldspar by the same signs, inde- 

 pendently of color. 



So we find in this bowlder three different minerals, and 

 their names are Quartz, Mica, and Feldspar. These three min- 

 erals mixed together form the rock Granite. There are sev- 

 eral varieties of granite, according to the species of mica ; 

 according to the colors of the quartz and feldspar; according 

 to coarseness of the constituents; according to the relative 

 proportions of the three ingredients. But they are all gran- 

 ites. If, however, the minerals are not uniformly mixed ; if 

 they are ranged in courses, the rock is stratified, and it is not 

 a proper granite, though quarrymen and builders often call it 

 granite. Properly, it is Gnei-ss (Nice). If the mica is al- 

 most or completely wanting in a granite-like rock, the rock is 

 Granulite. When a gneiss-like rock contains very little feld- 

 spar, it is Mica Schist (SI list). 



Now, let us examine another bowlder, with a similar ap- 

 pearance, but in which the dark mineral is not mica. Be 

 sure, first of all, that we have quartz and feldspar in it. Then, 

 if the dark mineral is not scaly, it is probably Hornblende. 

 It may be nearly black, or greenish-black, or dark green. It 

 may be in grains, or in flat-sided fragments showing an indistinct 

 fibrous structure. It can be scratched, giving a pale bluish-green 

 streak. Now, a rock with these constituent minerals Quartz, 

 Feldspar, and Hornblende, is Syenite so called because the rock 

 quarried by the ancient Egyptians at Sye'ne was of this kind. 

 Many persons call this granite also. The * ' Quincy granite/' near 

 Boston, is a syenite. Often syenite contains also some mica. This 

 is the case with the "obelisk," in Central Park, New York, 

 and the Mormon Temple, in Salt Lake City. If the constit- 

 uent minerals tend to arrangement in courses, the rock is 

 stratified, and we call it Syenitic Gneiss. If the quartz is want- 

 ing, or nearly so, the rock is Hyposyenite when the feldspar is 

 of the common kind, and Diorite when otherwise. When 



