KINDS OF ROCKS. 445 



I. NOT CONTAINING NEPHELITE. 



1. Syenyte. Quartz-Syenyte.— A granitoid rock consisting of 

 hornblende and orthoclase, with or without quartz. Oligo- 

 clase and biotite are often present. The quartziferous va- 

 riety, or quartz-syenyte, includes the syenyte of the obe- 

 lisks and pyramids of Egypt. Like that, the rock is often 

 flesh-colored ; but whitish and grayish varieties are also 

 common. The Saxon syenyte, without quartz, afforded 

 Silica 59*83, alumina 16*85, iron protoxide 7*01, lime 4*43, 

 magnesia 2-61, potash 6*57, soda 2*44, water 1*29, and Gk = 

 2*75-2*90. Metamorphic and eruptive. Similar varieties 

 occur under both divisions of syenyte. 



Varieties. — a. Porphyritic. b. Albitic ; containing albite in addi- 

 tion to the constituents of true syenyte. c. Oligoclase -bearing, d. Mi- 

 caceous : containing disseminated black mica, which, is usually bio- 

 tite, and. sometimes lepidomelane. e. Garnetiferous. f. Epidotic ; 

 containing disseminated epidote. The gray "granite " of Quincy, 

 Massachusetts, south of Boston, extensively quarried for architectural 

 purposes, is a quartz-syenyte, consisting of orthoclase, black to dark 

 green hornblende, and quartz, with some triclinic feldspar. Quartz- 

 syenyte occurs also in the Frankenstein Cliff, five miles south of 

 White Mountain Notch ; also in Mount Chocorua, N. H. ; in the Ar- 

 chaean of Canada, at Grenville, a red kind containing very little quartz, 

 and a similar rock on Barrow Island, St. Lawrence, but containing 

 much quartz and little hornblende. Syenyte without quartz is a rare 

 rock in Eastern North America. It occurs in Nevada. 



The name Syenites is used for this rock by Pliny, who adds that it 

 was also called "pyrrhopoecilon"— this appellation, meaning fire-red 

 variegated, referring to its being brightly spotted with rose-red. The 

 quarries in the vicinity of Syene (the modern Assouan), whence the 

 Egyptians obtained this stone for their obelisks, columns, statues, 

 sphinxes, sarcophagi, and the lining of their pyramids, are of great 

 extent ; and in one of them there is an unfinished obelisk in its origi- 

 nal position. They are situated to the south of Syene, and between 

 that place and the island of Philoe. The rock consists chiefly of red 

 feldspar and grayish quartz, with oligoclase, some black hornblende, 

 and a little black mica. An analysis by Delesse obtained Silica 

 70*25, alumina 1(3 00, iron oxide with some manganese 2 50, lime 160, 

 expelled on ignition 465, magnesia and alkalies by loss 9 00= 100. 

 More remote from Syene the rock loses its hornblende and becomes 

 a granite. 



The Scotch syenyte, so much used for monuments, is quartz-syenyte. 

 It occurs both red and dark gray, and the former is closely like the 

 Egyptian syenyte. 



Werner applied the name "syenyte" to the quartzless syenyte of 

 Plauenschen-Grunde, Saxony, an analysis of which is given above (a 

 rock he afterwards called " greenstone "). G. Rose used the term for 

 the quartz-syenyte. Other German lithologists have followed Werner, 

 calling the quartz-syenyte, hornblende-granite. It seems best to draw 



