450 DESCRIPTIONS OP ROCKS. 



6. PYROXENE AND SODA-LIME-FELDSPAR SERIES. 



1. Augite-Andesyte. — Contains the same triclinic feldspar 

 as andesyte, but augite is present in place of hornblende. 

 Amount of silica obtained in analyses about 55 to 58 per 

 cent. Texture crystalline-granular to aphanitic ; colors dark 

 gray to greenish-black and brownish-black. G. = 2 -65 - 2 -90. 

 Eruptive. 



Varieties. — There are two series : A. Ordinary, that is, without 

 chrysolite, or only in traces. B. Chrysolitk, chrysolite being in 

 disseminated grains or crystals. Under each there are varieties : 

 a. anhydrous ; b. hydrous, or chloritk, and feeble in lustre ; and 

 c. amygdaloidal, as well as chloritk. Again, each of these varieties 

 may be porpfiyritic. To the hydrous rock, and especially the chryso- 

 litic, the term Melaphyre is sometimes applied. 



Quartz- Augite- Andesyte is described by Zirkel as occurring in Pali- 

 sade Canon, in Nevada Plateau ; it contains yellowish-brown augite, 

 some biotite, some grains of quartz. Silica 62*71 per cent. 



2. Gabbro or Hyperyte. (Gabbro, in part.). — A basic grani- 

 toid rock in part, consisting of cleavable labradorite with dis- 

 seminated pyroxene, or a granular crystalline aggregate of 

 the two minerals. The pyroxene is often foliated, and has 

 been improperly called hypersthene. In place of labrador- 

 ite, the feldspar is sometimes andesite, and sometimes anor- 

 thite. Color, dull flesh-red to brownish-red, also dark-gray, 

 to grayish-black. Tough. G. =2 -7-3-1, varying with tho 

 proportion of pyroxene, which is sometimes small. Con- 

 tains also magnetite or titanic iron. 



The name Gabbro has been applied to this rock ; also to a coarsely 

 granular igneous rock, consisting chiefly of labradorite and foliated 

 pyroxene, referred beyond to doleryte ; to euphotide ; and, by the 

 Italians, formerly to serpentine. Ferber, in his "Briefe" (1773), says 

 (p. 98): Gabbro of Florence is the same as the rock called "sachsi- 

 schen Serpentin, in Deutschland," that is, the serpentine of Zoblitz. 

 Again, on page 330. he says that Mt. Impruneta, seven Italian miles 

 from Florence, consists of Gabbro. or the so-called Saxon serpentine, 

 and he alludes to the occurrence in it of diallage and amianthus, and 

 the presence also " der sogenannte Granitone " "in horizontalen 

 Schichten in den Gabbro-Bergen," which sometimes consisted " aus 

 weissem Feldspat, welcher grosse Parallelepipeden formirte," though 

 usually containing diallage. 



Varieties. — a. Granitoid ; the feldspar in distinct cleavable grains 

 or masses, b. Fcldspathose ; the pyroxene feeble in amount, c. Chry- 

 solitk ; contains disseminated chrysolite, d. Anorthitic, or Tractolite ; 

 anorthite replaces the labradorite* 



Includes the so-called hypersthenyte of the Adirondacks, Canada, and 

 Norway. Occurs also in. the Laramie Hills, Colorado, a kind which 

 afforded, on analysis. Silica 52 14, alumina 29 17, iron oxide 3 26, mag- 

 nesia 0'76, lime iO 81, soda 3*02, potash 098, ignition 0'58 = 100*92. 



