84 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
feet and a lower one of 35 feet, separated by about 25 feet of small ribboned material, 
the measurements being taken along the cleavage. In general, the beds range from 
3 to 30 feet in thickness, measured at right angles to the bedding. 
The Slatington slate is a very dark bluish gray. To the unaided eye it has a some- 
what tine texture and cleavage surface, but it is almost lusterless. It is carbonaceous 
or graphitic and slightly magnetitic. The sawn edges show little if any pyrite. It 
effervesces in cold dilute hydrochloric acid, is sonorous, and has some argillaceous 
odor. After prolonged exposure this slate becomes at first a dark gray and finally 
various shades of cream and coffee color, but the rapidity and degree of discoloration 
differ in different beds. Fissility fine. 
Under the microscope it shows a matrix of muscovite (sericite) with a brilliant 
aggregate polarization, obscured, however, by much carbonate and carbonaceous 
matter. There are many angular grains of quartz up to 0.04; rarely one of plagio- 
clase; a few scales of chlorite, interleaved with muscovite, or of each separately, up 
to 0.08 mm.; spherules of pyrite up to 0.012, rarely 0.02 mm., numbering about 130 
per square millimeter; very abundant rutile needles. 
The principal constituents, arranged in descending order of abundance, appear to 
be muscovite (sericite), carbonate, quartz, kaolin, pyrite, rutile, carbonaceous or 
graphitic matter, magnetite. 
The following analyses were made by Dr. W. F. Hillebrand, chemist of the United 
States Geological Survey — A from the Lower Franklin bed, Old Franklin quarry, 
Slatington; B from the Washington bed, Hazel Dell quarry No. 1, Slatington. 
Analyses of slates from Lehigh Cowiti/, I'a. 
Si0 2 (Silica) 
A1 2 3 (Alum ina) 
Fi '._,().; ( Ferric oxide) 
FcO (Ferrous oxide) 
Mgi » 1 Magnesia) , 
CaO (Lime) 
Na,<> (Soda) 
K 2 (Potassa) 
HoO (Water below 110° C.) 
H 2 (Water above 110° C.) 
Ti() 2 (Titanium dioxide) 
Zr0 2 (Zirconium dioxide) 
C( » 2 (Carbon dioxide) 
P 2 5 (Phosphoric oxide) 
Cr.jO.'j ( Chromium oxide) 
Mm » 1 Manganous oxide 1 
BaO (Baryta) 
SrO (Strontium oxide 
LLO (Lithia) 
FeS 2 (Pyrite) 
C. (Carbon of carbonaceous matter) 
Specific gravity (21° G.) 
A (complete) 
56.38 
15. 27 
M.67 
b 3. 23 
2.84 
4.23 
1.30 
3. 51 
.77 
4.09 
.78 
Trace? 
3. 67 
.17 
Trace? 
.09 
.08 
Trace. 
Trace. 
el. 72 
100. 39 
2.783 
B (partial). 
. r )C. 85 
a L5.24 
5. 52 
2.93 
4. 24 
1.38 
3. 34 
No! 
3. 58 
('') 
Tracel 
Not est. 
Not est. 
Not est. 
Not esi 
''1.72 
Not est. 
96.12 
2.780 
" Including P 2 5 . 
''Approximate. 
c A.S F<-.,<> ;: . 
''Included iu Al 2 (> :j . 
elncl. 0.92 of sulphur. 
The considerable amount of carbonate indicated both by the analyses and the 
microscopic examination and the discoloration due probably to the ferrous part of 
that carbonate are objectionable features in the Slatington slates, but their fine cleav- 
