KINDS OF ROCKS. 73 



graduates into chlorite slate, c. Garnetiferous. d. Pyritiferous ; contains pyrite in 

 disseminated grains or crystals, e. Magnetitic; contains disseminated magnetite, e. 

 Quartzytic; consists largely„of quartzyte, or is a quartzyte rendered schistose and 

 partly pearly by the presence of a hydrous mica. 



6. Argyllitic Hydromica Schist [Hydromica Argillyte). — Includes the Argillyte 

 or clay-slate which has the composition nearly of a hydrous mica, like that of the White 

 Mountain Notch, where much of it is Andalusitic. 



7. Paragonitk Schist or Slate. — Consists largely of the hydrous soda mica 

 called paragonite; but in other characters resembles hydromica slate. 



8. Miascvte. — Granitoid, and containing massive nephelite (elaeolite) along with 

 orthoclase, biotite, some quartz, and also sodalite. 



9. Felsyte (Euryte, Petrosilex). — Compact orthoclase with often some quartz in- 

 timately mixed, flint-like in fracture. Opaque. Colors grayish-white to red and brown- 

 ish-red. Sp. gr. = 2G-2-7. 



Varieties. — a. Porphyritic Felsyte, or Porphyry ; containing the feldspar in 

 small crystals distributed through the compact base ; color red, and of other shades, 

 b. Conglomerate felsyte ; containing pebbles, as at Marblehead, Mass., and in the 

 White Mountains, c. Quartzose ; containing quartz in grains; often called quartz felsyte, 

 and quartz-porphyry, d. Elvanyte ; essentially a quartzose felsyte, of gray, bluish-gray 

 to brown and red colors, and often containing disseminated grains or crystals of quartz 

 and feldspar. The feldspar is sometimes oligoclase. Some compact slate-rock has the 

 same composition. 



10. Porcelanyte, or Porcelain-Jasper, is a baked clay, having the fracture of flint 

 and a gray to red color : it is somewhat fusible before the blowpipe, and thus differs 

 from jasper. Formed by the baking of clay-beds, when they consist largely of feldspar. 

 Such clay-beds are sometimes baked to a distance of thirty or forty rods from a trap 

 dike, and over large surfaces by burning coal beds. 



3. Hornblende Series. Pyroxene Series. 



1. Contain orthoclase : and hornblende as prominent constituents; the hornblende often 

 associated with biotite, and sometimes replaced by epidote. 



1. Syenyte, Quartz-syenyte. — A granitoid rock consisting of hornblende and 

 orthoclase, with or without quartz. The quartziferous variety, or quartz-syenyte, is the 

 original syenyte of Syene, Egypt. Like that, the rock is often flesh-colored; but whit- 

 ish and grayish varieties are also common. Under the quartz-syenyte and quartzlesE 

 syenyte there are the following 



Varieties. — a. Porphyritic. b. Albitic ; containing albite in addition to the con- 

 stituents of true syenyte. c. Oligoclase-bearing. d. Garnetiferous. e. Epidotic ; con- 

 taining disseminated epidote. 



2. Syenyte-gneiss. — Like gneiss in aspect and schistose structure; and also in con- 

 stitution, except that hornblende replaces mica. Graduates into 



3. Hornblende-schist, a schistose rock consisting chiefly of hornblende. 



4. Unakyte. — A flesh-colored, granitoid rock consisting of orthoclase, quartz, and 

 epidote. From the Unaka Mountains, N. Carolina, and E. Tennessee. 



5. Zircon-syenyte. — A crystalline granular rock consisting of orthoclase, micro- 

 cline, little hornblende, crystals of zircon, and some elaeolite. 



Foyayte and Ditroyte are other orthoclase rocks containing elaeolite with some 

 hornblende: but they are described as eruptive. 



2. Contain a triclinic feldspar and hornblende as prominent constituents. 



1. Dioryte. Quartz-dioryte. — The triclinic feldspar, one of the acidic (rich in 

 silica) species, albite or oligoclase. Texture, granitoid to fine-grained or compact. 

 Color often grayish-white to greenish-white, for the coarser kinds; olive-green to black- 

 ish-green for the finer. Very tough. Sp. gr. 2-7-3-0. 



Varieties. — a. Granitoid; granite-like in texture, b. Compact; or fine-grained, 

 with the feldspar grains scarcely distinguishable, c. Porphyritic ; the feldspar in crys- 

 tals in a compact base. d. Slaty ; a dioryte slate, usually chloride e. Quartzose, or 



