430 EEPORT ON NATIONAL MUSEUM, 1886. 



(4) LIPARITES OF THE VARIOUS STATES AND TERRITORIES. 



Near Mokelumne Hill, iu Calaveras County, Cal., rliyolite occurs in 

 several different colors, and lias been quarried to some extent for use in 

 the immediate vicinity. It is also abundant in Colorado, New Mexico, 

 Nevada, Utah, and other of the Western States and Territories. 



The glassy variety of rliyolite called obsidian is very abundant in cer- 

 tain parts of the West, and though as yet no attempt has been made to 

 utilize the material there would seem no good reason for its not being 

 used in small pieces for the finer kinds of decorative work. The rock, 

 which is a natural glass formed by the rapid cooling of a molten mass, is 

 of various colors, black, red, and greenish, and often beautifully spotted 

 and streaked. From the Yellowstone National Park, Glass Butte, Or- 

 egon, and other sources, the Museum has received specimens of red 

 obsidian spotted and streaked with black wavy lines in a way that is 

 highly ornamental. The stone occurs naturally in a badly jointed con- 

 dition and could be obtained only in pieces of small size. Owing to its 

 glassy fracture also it could be worked only with plain flat surfaces, 

 but as it takes a high glass like polish, it would be very desirable for 

 tops of small stands, paper-weights, and inlaid work. 



H.— THE SYENITES, TRACHYTES, AND PHONOLITES. 



(1) DEFINITION OF SYENITE. 



Under the name of Syenites are here included those rocks consisting 

 essentially of orthoclase with or without one or more of the accessory 

 minerals, mica, hornblende, or augite. They differ from granites only 

 in the absence of quartz, and otherwise present a i)recisely parallel 

 series. Thus we may have mica syenite (minette), hornblende syenite, 

 augite syenite, etc.* 



(2) LOCALITIES OF SYENITE. 



At the present time syenites are but little quarried in this country, 

 though there would seem to be no lack of material and of good (piality. 



In and about Portland, Me., there occur in the glacial drift many 

 bowlders of a beautiful syenite, the exact source of whi(!h is not known 

 to the author, but Avhich can not be far to the northward. The ro(;k 

 consists mainly of bright lustrous gray orthoclase and coal-black horn- 

 blende, with occasionally a little black mica. In texture it is not too 



* Formerly it was customary to call hy the :iame syenito a rock consisting of qnart z 

 liornblendc, and orthoclase, or what is now called a hornhlcnde granite. The name 

 takes its origin from Syene, Egyi)t, wliere a rock supjiosed to ansvrer this description 

 was originally quarried. Investigation has, however, shown that the Syene rock eon- 

 tains more mica than hornblende, and hence at best can not be chxssed as a true sye- 

 nite even according to the old definition. According to recent lithologists the Syene 

 rock is a hornblende mica granite, while true syenite, aa above stated, is a quartzless 

 rock. 



