KINDS OF ROCKS. 77 



2 A hornblende and angite series, the species containing as prominent ingredients, 

 ^esides a feldspar, hornblende or augite (iron-bearing minerals), with often magnetite 

 or titaniferous iron, and hence of high specific gravity (2 , 7-3"5). 



3. A chrysolitic series, the species containing chrysolite and other ingredients, with 

 little or no feldspar. 



1. Feldspathic Series. 



1- Granite. — Similar to metamorphic granite (p. 71). 



2. Granuiyte. — Similar to metamorphic granulyte (p. 72). 



3. Felsyte. — Similar to metamorphic felsyte (p. 73) in its aphanitic texture. 

 Colors gray, brown, and red. Consists of orthoclase, with or without some quartz in- 

 timately blended; also, in other cases, in part of oligoclase. 



Varieties. — A. Orthoclase felsyte ; B. Oligoclase- bearing felsyte; and under each 

 the following kinds : a. White or gray. b. Red or brownish-red. c. Porphyritic ; with 

 the base red or brown or of other shades, d. Fine-granular, e. Cellular or amygdal- 

 oidal. 



Some felsyte has nearly the aspect of trachyte, with which it is identical in composi- 

 tion. 



4. Phon lyte (Clinkstone). — Compact, of grayish-blue and other shades of color, 

 more or less schistose or slaty in structure ; tough, and usually clinking under the 

 hammer like metal when struck, whence the name. Sp. gr. 2-4-2-7. Consists of glassy 

 feldspar (orthoclase or oligoclase), with nephelite and some hornblende ; G. Jenzsch 

 gives, for the composition of the Bohemian phonolyte, — Sanidin (glassy orthoclase) 

 53-55, nephelite 31'76, hornblende 9-34, sphene 3 - 67, pyrite 0-04. Under treatment with 

 acids, the nephelite is dissolved out. Nosean and hauyne occur in some phonolyte. 



5. Trachyte. — Consists mainly of feldspar, which is partly in glassy crystals, 

 either sanidin or oligoclase ; and owing to the angular forms of the glassy feldspar and 

 the porosity of the rock, the surface of fracture is rough, whence the name from the 

 Greek, rpaxvs, rough. Color ash-gray, greenish-gray, brownish-gray, but some- 

 times yellowish and reddish. Sp. gr. 2-5-2-7. Besides the feldspar, there are distrib- 

 uted somewhat sparingly through the mass, in many kinds, minute needles of horn- 

 blende, crystals of biotite mica, magnetite; sometimes nephelite, hauyne, tridymite. 

 Apatite exists in the rock in microscopic forms, and there are also particles of the 

 rock in a glassy state. Sometimes contains augite and has higher specific gravity. 



Varieties. — The two principal divisions are: A. Sanidin-trachyte, in which the 

 mass is chieflv sanidin; and B. Oligoclase trachyte, or domyte,\n which it is partly oligo- 

 clase; but the two graduate into one another. Both occur porphyritic with tabular 

 crystals of feldspar; and in the latter (as at Drachenfels) the tables are sanidin. Each 

 may contain free quartz, becoming thereby quartz-trachyte. Each graduates also into 

 vesicular or scoriaceous trachyte. 



Trachyte and quartz-trachyte graduate into felsyte like volcanic rocks of like consti- 

 tution, porphyritic, or not so. The latter sometimes graduates into rocks of semi-glassy 

 nature called 



6. Peaklstone, when somewhat pearly in lustre ; Pitchstone, when having a 

 pitch-like lustre; and these into the glassy volcanic material called Obsidian. These 

 glassy rocks often contain spherules which are concretions consisting of feldspar with 

 some quartz. Pumice is a light, porous, feldspathic scoria, with the pores capillar}' and 

 parallel. Ordinary obsidian, that consists ch'efly of feldspar, and is hence nearly free 

 from iron, belongs here, the rest of it belonging with the augitic igneous rocks. Obsid- 

 ian, pitchstone, pearlstone, and some other kinds of igneous rocks have been classed 

 together and called rhyolyte, from the Greek pvw, I flow, because showing in then- 

 microscopic structure, if not also externally, that thev have flowed as lavas. But this 

 fiuidal feature belongs to rocks of very different kinds, and is only of varietal value. 



7. Leucityte. — A grayish rock consisting chiefly of leucite in a felsitic state, with 

 disseminated leucite crystals. Occurs at Point of Rocks, Wyoming Territory, accord- 

 ing to King and Zirkel. 



