I70 ALBERT JOHANNSEN 



12 per cent, andesine 59.2 per cent, pyribole 16.8 per cent, mica 

 3 . 8 per cent, and other accessories 7 . 9 per cent. 

 Syn. : Quartz-diorite. 

 Dacite Stache. The name dacite was given by Stache^ 

 to certain older quartz-trachytes, found in Siebenbiirgen (Dacia), 

 which contain oUgoclase and pyroxene and which were thus 

 thought to be separated from the younger quartz-trachytes or 

 rhyoHtes which contain sanidine and biotite. The term has been 

 variously used by different petrographers, some applying it only to 

 extrusive plagioclase rocks with quartz phenocrysts, others includ- 

 ing rocks whose only quartz is in the groundmass ; some requiring 

 the presence of pyroxene, others including rocks with biotite. 

 In general the name has come to mean quartz-andesite, the extrusive 

 equivalent of quartz-diorite, and it is so used here. 



Syn. : Quartz-andesite. 

 (2212) Syenite. The name syenite was used at least as long 

 ago as the time of Phny,^ and was apparently in common use in his 

 day for the rocks from Syene (Assuan), Egypt. "Circa Syenen 

 vero Thebaidis Syenites," he says, "que ante pyrrhopoecilon voca- 

 bant," that is, spotted with red. Werner^ appHed the term Sienit 

 to the hornblende-bearing rock from near Dresden, under the 

 impression that the two were the same. It was later found that the 

 Syene rock contains quartz, is, in fact, hornblende-granite, while 

 the Dresden rock is practically quartz-free. Some writers conse- 

 quently used the term syenite for hornblende-granite, but gener- 

 ally it was used for quartz-free orthoclase rocks in the sense of 

 Werner. Rosiere" found that the rock of Mount Sinai is of the 

 quartz-free variety and therefore proposed that the name be 

 changed to sinaite. The older term, however, was in such common 

 use that this suggestion was not followed. 



' G. Stache, " Quarztrachyte Siebenbiirgens," in Fr. von Hauer and G. Stache, 

 Geologic Siebenbiirgens (1863), pp. 56, 70, 79. 



^C. Plinii Secundi Naturalis historiae xxxvi. cap. viii. In the edition Lugd. 

 Batav. Roterodami, Ao. 1668, p. 647. 



3 " Vermischten Nachrichten," Bergmdnnisches Journal, II (1788), 824. 



4 J. F. d'Aubuisson de Voisins, Traite de geognosie (Strasbourg et Paris, 1819), 

 p. 21. 



