448 DESCRIPTIONS OF ROCKS. 



oligoclase or andesite and hornblende, with G.=273 — 2 '80, and afford- 

 ing 55 to 61 per cent, of silica ; it occurs in the Peak of Teneriffe, on 

 Liscanera I. near Stromboli, and on some parts of Etna. Another rock 

 included under this name, found at Stromboli, Rocca Monfina, and 

 Tunguragua in Quito, contains augite in place of hornblende, with 

 oligoclase or labradorite, and is near doleryte, A third rock described 

 under this name by Ludwig is augiiic trachyte, the feldspar being 

 sanidin. Trachyte graduates into andesyte, augite-andesyte, doleryte, 

 as well as granite. 



3. Labradioryte. (Labradorite-Dioryte, Greenstone in part.) 

 — The feldspar one of the basic (poor in silica) species, la- 

 bradorite or anorthite. Texture usually fine-grained, some- 

 times crypto-crystalline. Color light grayish-green to dark 

 olive-green, blackish-green or gray, and sometimes black. 

 Very tough. G-. =2*8-3*1. Often contains chlorite and 

 magnetite. Often has associated with it beds of serpentine 

 or ophiolyte. Metamorphic and eruptive. 



Varieties. — a. Granular crystalline, b. Compact, or fine-grained ; 

 of dark green color ; constituent minerals not distinct, c Porphyri- 

 tic ; the feldspar in whitish or greenish- white crystals disseminated 

 through a fine-grained base, making a greenish "porphyry;" its 

 crystals sometimes anorthite. d. Pyroxenic; containing some dissem- 

 inated pyroxene, e. Magnetitic ; containing magnetite or titanic iron. 

 Occurs in the Urals ; to the west of Xew Haven, Conn., both massive 

 and porphyritic ; in Littleton, N. H. A porphyritic variety of the 

 rock near Xew Haven — a metamorphic rock — afforded Hawes, Silica 

 48"61, alumina 17*81, iron sesquioxide 0*25, iron protoxide 8'46, man- 

 ganese protoxide 20, lime 1116, magnesia 770, soda 2*77, potash 

 0-47, water 1-63, titanium dioxide 1-35 = 100'47; G. =3-01. A com- 

 pact non-porphyritic variety from the same formation, collected on 

 Stoeckel's farm, afforded Hawes, Silica 50 "33, alumina 14*5 7, iron ses* 

 quioxide 2 48, iron protoxide 8*31, manganese protoxide 0'46, magne- 

 sia 7*02, lime 11*13, soda 3"04, potash 044, water 0*78, titanium diox- 

 ide 1-70, chromium oxide 0'78=100'89 ; G. =3'04. The crystals of the 

 porphyritic variety, according to an imperfect analysis by E. S. Dana, 

 consist of anorthite. 



4. Corsyte. — A granitoid rock, consisting chiefly of anor- 

 thite and hornblende, with some quartz and biotite. From 

 Corsica. 



Teschenite is bluish-green, and chiefly consists of anor- 

 thite, hornblende, and augite, the hornble de sometimes in 

 large black prisms ; also contains analcite. From Teschen, 

 Austria, 



5. Xsenite. — Contains a triclinic feldspar and hornblende, 

 with much nephelite and nosean, and some magnetite. 

 From the Eisbach (Isena) district in the Westerwafd, West 

 Germany. 



