54 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
This is a very superior roofing slate, with a remarkably fine cleavage and not liable 
to discolor on exposure, but its strength and its behavior under frost should be tested. 
Dark-reddish slate from Mena, near Big Forks. In color this slate is somewhat 
darker than the "red" slate of New York. To the unaided eye it has a minutely 
granular texture and a roughish, speckled, almost lusterless surface. Contains very 
little magnetite; does not effervesce with cold dilute hydrochloric acid, is sonorous, 
splits readily, and has some argillaceous odor. Under the microscope it shows a 
matrix of muscovite (sericite), with brilliant aggregate polarization, quartz grains 
ranging up to 0. 025 mm. muscovite and chlorite scales, and abundant hematite in 
minute dots. There are also rhombs, from 0.1 to 0.2 mm., of chlorite and rhodo- 
chrosite, probably pseudomorphs after ? No other carbonate. 
The constituents, arranged in descending order of abundance, appear to be mus- 
covite (sericite), hematite, kaolin, quartz, chlorite, rhodochrosite?, and magnetite. 
This slate compares favorably in texture with the New York "red" slate. 
Reddish slate from Mammoth red and Lost Hannah beds (exact locality not given). 
Color lighter than above, but not quite so red as the New York slate. To the unaided 
eye has a fine texture and a fine cleavage surface, but no luster. Contains very little 
magnetite; does not effervesce with cold dilute hydrochloric acid, is sonorous and 
fissile, has some argillaceous odor. 
Under the microscope it shows a matrix of muscovite (sericite), with brilliant 
aggregate polarization, quartz grains up to 0.03 mm., muscovite and chlorite scales, 
abundant hematite pigment, and no carbonate. 
The constituents, arranged in descending order of abundance, appear to be musco- 
vite (sericite), hematite, kaolin, quartz, chlorite, and magnetite. 
This is a finer and softer slate than the dark red, and should be tested for strength 
and frost resistance. 
Greenish-gray slate from Mena. In color this resembles the "sea-green" slate of 
Vermont. To the unaided eye it has a fine texture, a roughish cleavage surface, and 
a waxy luster; does not show pyrite on sawn edge, contains very little magnetite; 
does not effervesce with cold dilute hydrochloric acid, and is somewhat sonorous. 
Under the microscope it shows a matrix of muscovite (sericite), with a brilliant 
aggregate polarization and is of very fine texture and homogeneity, but the cleavage 
is crossed at an angle of 13° by a very close bedding foliation and also by an obscure 
slip or "false" cleavage at about 40°. Contains very few and very minute quartz 
grains, no carbonate, several pseudomorphic rhombs of chlorite 0.08, mm., and has 
a slight argillaceous odor. 
The constituents, arranged in descending order of abundance, appear to be musco- 
vite (sericite), quartz, kaolin, chlorite, and magnetite. 
The two extra foliations are likely to prove directions of weakness. 
Light-greenish slate from Mammoth red bed, locality not designated. This is more 
greenish than the above, to the unaided eye has an exceedingly fine texture and a 
very fine, almost lusterless cleavage surface; shows pyrite on sawn edge, contains a 
little magnetite; does not effervesce with cold dilute hydrochloric acid, is sonorous, ) 
very fissile, and has a slight argillaceous odor. 
Under the microscope it shows a matrix of muscovite (sericite), with a brilliant 
aggregate polarization and great evenness of texture. A very minute bed of quartz 
grains, chlorite, and muscovite lies in the cleavage, which is, therefore, the bedding 
also. The grain is indicated by the transverse position of some of the muscovite 
scales. Quartz not very abundant, but occurs in grains up to 0.037 mm. Entile . 
needles abound from 0.0028 by 0.0009 up to 0.014 by 0.0014 mm. Muscovite and] 
chlorite scales occur, the latter producing the green color. There are some opaque 
granules (limonite? and pyrite), occasional lenses, 0.14 mm. long, of a central mass 
(probably rhodochrosite), with secondary muscovite at both ends. No other car 
bonate. Shows a number of tourmaline prisms up to 0.025 by 0.008 mm. 
