KINDS OF ROCKS. 441 



feeling greasy to the fingers ; pearly to faintly glistening in 

 lustre ; whitish, grayish, pale greenish in color, and also of 

 darker shades. For analyses of hydrous micas see page 313. 

 Metamorphic. 



This rock used to be called talcose slate, but, as first shown by Dr. C. 

 Dewey, it contains no talc. It includes Paropkite schist, Damourite 

 slate and Sericite slate {Glanz-Schiefer and Sericit-Schiefer of the Ger- 

 mans.) 



Varieties. — a. Ordinary ; more or less silvery in lustre, b. Chlo- 

 ritic ; contains chlorite, or is mixed with chlorite slate, and has there- 

 fore spots of olive-green color; graduates into chlorite slate, c. Gar- 

 netiferous. d. Pyritiferous ; contains pyrite in disseminated grains or 

 crystals, e. Magnetiiic ; contains disseminated magnetite, f . Quart- 

 zytic; consists largely of quartzyte, or is a quartzyte rendered schistose 

 and partly pearly by the presence of hydrous mica, as is well seen in a 

 ridge northeast of Rutland, Vermont, which consists partly of quartzyte 

 and partly of hydromica schist. 



7. Paragonite Schist. — Consists largely of the hydrous 

 soda mica called paragonite (p. 314); but in other characters 

 resembles hydromica schist. Metamorphic. 



8. Minette. — Brown to black, fine-grained, compact, not 

 distinctly schistose ; consisting of biotite (according to 

 the description and analysis of Delesse) and orthoclase ; 

 contains also a little hornblende. Occurs in beds in the 

 Vosges, France, associated with granite, syenyte, and other 

 crystalline rocks. Sometimes feebly porphyritic and small- 

 concretionary, the concretions consisting mainly of ortho- 

 clase. Made eruptive by Delesse, and metamorphic by some 

 later authors. Approaches argillyte in aspect. 



9. Greisen. — Massive, without schistose structure. A mix- 

 ture of granular quartz and mica, in scales. The mica may 

 be muscovite, lepidolite, or biotite. It is a granite with the 

 feldspar left out, and occurs in regions of gneiss, granite, 

 or quartzyte, and sometimes graduates into these rocks. 

 Metamorphic. 



Occurs in characteristic form at Zinnwald, in the Erzgebirge, where 

 it sometimes contains tin ore as an accessory ingredient, and is fre- 

 quently penetrated by veins of tin ; also in the tin ore regions of 

 Schlackenwald and Cornwall. Occurs in the region of quartzyte, horn- 

 blendic rocks and gneiss, of Upper Silurian age, between Bernards- 

 ton, Mass , and Vernon, Vt., within three miles northeast of the former 

 place, and also near Vernon ; but at this place it contains usually a 

 little hornblende, making it a very tough rock, and is intermediate 

 between the quartzyte, hornblendic rock and mica schist of the region. 



10. Mica- Argillyte or Mica-Phyllyte. — Includes the part of 

 argillyte (p. 428) which has the composition nearly of a hy- 

 drous mica, like that of the White Mountain Notch, where 



