KINDS OF ROCKS. 73 



(7.) Serpentine (p. 55). — A massive uncleavable rock, of dark- 

 green to greenish-black color, easily scratched with a knife, and often 

 a little greasy to the feel when a surface is smoothed. Although 

 generally of a dark-green color, it is sometimes pale grayish and 

 yellowish green, and mottled. 



(8.) Ophiolyte (or Verd-antique marble). — A variegated mixture 

 of serpentine and either carbonate of lime {calcareous ophiolyte), do- 

 lomite (dolomitic ophiolyte), or carbonate of magnesia or magnesite 

 (magnesitic ophiolyte). Color, dark green, mottled with lighter green 

 or white. 



It often contains chromic iron sparsely disseminated through it, forming irregular, 

 black, submetallic spots; also some talc, asbestus, sahlite; and analysis often detects 

 nickel as well as chrome. T. S. Hunt has found both nickel and chrome in the ser- 

 pentines or ophiolytes of the Green Mountain range, in those of Roxbury, Vt., New- 

 Haven, Ct., Hoboken, N. J., Cornwall, England, Banffshire, Scotland, Vosges, France. 

 They occur also in the pyrosclerite and williamsite of Chester Co., Pa., and in the 

 antigorite of Piedmont. Hunt found no nickel in serpentine from Easton, Pa., Mont- 

 ville, N. J., Philipstown, N. Y., Modum, Norway, Newburyport, Mass., and none from 

 the Archaean series of rocks. 



(9.) Schillekyte, or Schiller rock, Diallage rock. — A dark-green to greenish- 

 black rock, made up of Schiller spar. It is often associated with serpentine, chlorite, 

 and talc-schist. 



6. Hydrous Aluminous rocks. 



These rocks consist largely of agalmatolite or pyrophyllite, and have a close re- 

 semblance to talcose and serpentine rocks in feel, hardness, and appearance. 



rAKOPHYTE. — Essentially agalmatolite (p. 58) in composition. Its fine-grained tex- 

 ture and somewhat soapy feel are its striking peculiarities. It occurs both as a slate 

 and as a rock, and the slate closely resembles talcose slate. The dysyntribyte of Shep- 

 ard, found in northern New York, is a rock variety. 



Pyrophyllytk and Pyrophyllyte Slate. — Like the preceding in appearance 

 and soapy feel, but having the composition of pj'rophyllite (p. 58). The color is white 

 and gray, or greenish white. Occurs in North Carolina; one of the varieties from the 

 Deep River region is used for slate pencils. 



7. Quartzose roclcs. 

 (1.) Quartzyte, or Granular Quartz Rock. — A hard, compact 

 rock, consisting of quartz grains or sand, and usually either white, 

 gray, or grayish-red in color. Sometimes contains disseminated feld- 

 spar or mica, and is often laminated or schistose. It is but a step 

 removed from ordinary sandstone, and owes its peculiarities to meta- 

 morphic agencies. It sometimes graduates into gneiss. 



(2.) Siliceous Slate. — A schistose, flinty, quartz rock, not distinctly granular in 

 texture. Sometimes passes into mica slate or schist. 



(3.) Chert. — An impure flint or hornstone rock, occurring imbedded in some 

 stratified rocks; also flinty siliceous rock, forming layers in siliceous schist or slates. It 

 often resembles felsyte, but is mainly quartz, and is therefore infusible. Colors 

 various. Sometimes oolitic. Kinds containing iron ore graduate into jasper and clay- 

 ironstone. 



(4.) Itacolumyte. — A schistose quartz rock, consisting of quartz grains with 

 \iydrous mica. On account of the mica in the lamination, the finer kind is sometimes 

 flexible, and is called flexible sandstone. 



