558 REPORT OF NATIONAL MUSEUM, 1890. 



length are not rare (specimens 26418 and 72884). Neither of the es- 

 sential constituents occur in the form of perfect crystals, while the 

 apatite, zircon, black mica, and pyroxenic constituents often present 

 very perfect forms. The cancrinite occurs both as secondary after the 

 eheolite and as a primary constituent in the form of long needle like 

 yellow crystals with a hexagonal outline. This last form is especially 

 characteristic of the Litchfield rock (see specimens Nos. 72884, 72885, 

 and 72880). The sodalite occurs both as crystals and in irregular mas- 

 sive forms, coating the walls of crevices, as shown in specimens 36342, 

 38845, 72884 and 72885, from Maine, and from Ditro, Transylvania. 



Classification and nomenclature. — Several varietal names have been 

 given to the rocks of this group as described by various authors. Mi- 

 ascite was the name given by G. Kose to the syenite occurring atMiask 

 in the Urals; Ditroite to that occurring at Ditro, in Transylvania (spec- 

 imens 36342, 38813, 38814, 38815 and 73110), and Foyaite by Blum to 

 that from Mount Foya in the province of Algrave in Portugal (speci- 

 mens 34817 and 34820). The name Zircon syenite has been quite appro- 

 priately given to the variety from Laurvig (specimen No. 36341), in 

 southern Norway, which is rich in this mineral. Tinguaite is the 

 name proposed for a varietal form from Serra de Tingua, proviuce of 

 Rio Janeiro, Brazil (specimens 69953, 70234, 70235, 70236 and 70240). 



Like the syenites proper, these are rocks of comparative rarity. The 

 following varieties and localities are represented : 



Near Hot Springs, Saline County, Arkansas, 27519 and 39188; Fourche Cove, Pulaski 

 County, Arkansas, 4874 and 4885; Litchfield, Kennebec County, Maine, 26418 

 and 35935; Ibid, with much cancrinite, 72884; Ibid, showing large patches of 

 sodalite (blue) and cancrinite (yellow), together with zircons, 72885 ; Marblehead, 

 Massachusetts, 37664; near Liberty ville, New Jersey, 36776. Serra de Tingua, 

 Brazil (Tinguaite), 69953, 70234, 70235, 70236, and 70240 ; Ilha do Cabo Frio, Rio 

 Janeiro, Brazil, 69944; Aroen, Langsundsfjord, Norway (with eukolit and rae- 

 linophane), 36340; Ibid (zirkon syenite), 36341 ; Little Aro, Barkevig and Laven, 

 Aroen, Langsundsfjord, Norway, 70405, 36336, 36337, and 36338; Laurvik, Nor- 

 way, 70400; Ditro, Transylvania (Ditroite), 38815 (with sodalite), 38813, 38814, 

 36342; Predazzo, Tyrol, 36340, 39184; Foya, Portugal (Foyaite), 34819 and 34820; 

 Picota, Portugal, 34817. 



Elseolite syenite porphyry (Liebnerite) near Predazzo, Tyrol, 36343; Viezena, Fassa 

 Thai, Tyrol, 73113. 



4.— The diorites (Greenstone in part). 



Diorite, from the Greek word dtopi^ecv, to distinguish. Term first 

 used by the mineralogist Hauy. 



Mineral composition. — The essential constituents of diorite are plagio- 

 clase feldspar, either labradorite or oligoclase, and hornblende or black 

 mica. The common accessories are magnetite, titanic iron, orthoclase, 

 apatite, epidote, quartz, augite, black mica, and pyrite, more rarely gar- 

 nets. Calcite and chlorite occur as alteration products. 



Chemical composition. — According to Zirkel, the average chemical 

 composition is silica, 52.66 ; alumina, 18.92 ; iron protoxide, 9.09 ; lime, 

 6.73; magnesia, 5. 12 ; potash, 2.42 ; soda, 3.71 ; water, 1.35 per cent. 



