440 DESCRIPTIONS OF ROCKS. 
4. Protogine, Protogine-gneiss.—Coarse to fine granular, 
eranite-lke or oneissoid in structure, and mostly the lat- 
ter; of a grayish-white to greenish-gray color; consists of 
quar tz, white or grayish- -white, rarely flesh-red, orthoclase, 
a dark green mica and often Nets. with some greenish- 
white tale, and white oligoclase. Metamorphic. 
The dark green mica approaches chlorite, as shown by Delesse, in 
its very large percentage of iron oxide (Ie, O, 21°31, #eO 5 03), but it 
gave him only U9u of water, with 6°05 of potash. Among accessory 
minerals are hornblende, titanite, garnet, serpentine, magnetite. In 
an analysis of the protogine as a whole, Delesse obtained Nilica 74-25, 
alumina 11:58, iron oxide 2:41, lime 1 08, water 0:97, leaving 10°01 for 
potash, soda and magnesia. From the region of Mont Blane and 
other paris of the Swiss Alps. : 
5. Mica Schist.—Consists largely of mica, with usually 
much quartz, some feldspar, and, on account of the mica, 
divides easily into slabs, that is, is very schistose. Usually 
both of the potash micas, muscovite and biotite, are present, 
and the latter (black mica) is commonly much the most 
abundant. The colors vary from silvery to black, according 
to the mica present. Often crumbles easily; and roadsides 
are sometimes spangled with the micascales. The dissemi- 
nated scales or crystals of biotite are sometimes set trans- 
versely to the bedding. Metamorphic. : 
VARIETIES.—a. Gneissoid ; between mica schist and gneiss, and 
containing much feldspar, the two rocks shading into one another. 
b. Hornblendic. c. Garnetiferous. d. Staurolitic. e. Cyanitic. f. An- 
dalusilic. g. Fibrolitic ; containing fibrolite. h. Tourmalinic. 1. Cal- 
careous ; limestone ocet urring in it in occasional beds or masses. 
j. Graphitic, or Plumbaginous ; the graphite being either in scales or 
impregnating generally the schist. I. Quurtzose; consisting largely of 
quartz. 1. Quartzytic ; a quarizyte with more or less mica, rendering 
it schistose. m. Specular, or Jtabyrite ; containing much hematite or 
specular iron in bright metallic lamelle or scales. In fine-grained 
mica schist, the scales cf mica are sometimes scarcely visible without 
a lens. 
6. Hydromica Schist—A thin-schistose rock, consisting 
either chiefly of hydrous mica, or of this mica with more 
or less quartz; having the surface nearly smooth, and 
feeling greasy to the fingers ; pearly to faintly glistening in 
lustre ; : ‘whitish, er ayish, pale greenish in color, and also of 
darker shades. For analyses of hydrous micas see page 313. 
Metamorphic. 
