GRANITE. 



351 



GEANITE. SYENITE. 



Granite consists of the three minerals, quartz, feldspar, 

 and mica. It has a crystalline granular structure, and usual- 

 ly a grayish-white, gray, or flesh-red color, the shade vary, 

 ing with the color of the constituent minerals. When it 

 contains hornblende in place of mica, it is called syenite , 

 hornblende resembles mica in these rocks but the laminae 

 separate much less easily and are brittle. 



Granite is said to be micaceous, feldspathic, or quartzose, 

 according as the mica, feldspar, or quartz, predominates. 



It is called porphyritic granite, when the feldspar is in 

 large crystals, and appears over a worn surface like thickly 

 scattered white blotches, often rectangular in shape. . 



Graphic granite has an appearance of small oriental cha- 

 racters oyer the surface, owing to the angular arrangement 

 of the quartz in the feld- 

 spar, or of the feldspar in 

 the quartz. 



When the mica of the 

 granite is wanting, it is 

 then a granular mixture 

 of feldspar and quartz, 

 called granulite or lepty- 



flZtC' (jrapldc Granite. 



When the feldspar is replaced by albite, it is called albite 

 granite. The albite is usually white, but otherwise resem- 

 bles feldspar. When replaced by talc, it is called protogine. 



Granite is the usual rock for veins of tin ore. It .con- 

 tains also workable veins of pyritous, vitreous, and gray 

 copper ore, of galena or lead ore, of zinc blende, of specu- 

 lar and magnetic iron ore, besides ores of antimony, cobalt, 

 nickel, uranium, arsenic, titanium, bismuth, tungsten, and 

 silver, with rarely a trace of mercury. The rare cerium and 

 yttria minerals are found in granite, and mostly frequently in 



The experiments of W. H. C. Bartlett, Lieut. U. S. Engineers, led 

 the following results. — Amer. J. Sci., xxii, 136, 1832. 



Granite, 

 Marble, 

 Sandstone, 

 Hammered copper, 



For 1° F. 

 •000004825 

 •000005668 

 •000009532 

 •000009440 



For 180° F. 

 •00086904 

 •00102024 

 •00171596 

 .00169920 



