36 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
Summarized analyses of roofing slates from New York, Vermont, and Pennsylvania 
Si0 2 (silica) 
Ti0 2 (titanium dioxide) 
ALO3 (alumina) 
Fe 2 :} (ferric oxide) 
FeO (ferrous oxide) 
CaO (lime) 
MgO (magnesia) 
K 2 (potassa) 
Na 2 (soda) 
C0 2 (carbon dioxide) 
FeS 2 (pyrite) 
H 2 (water above 110° C.) . . 
C (carbon) 
Sundry and water below 
110° c 
Total 
Specific gravity b 
Sea 
green. 
(3) a 
Vt. 
63.33 
.73 
14.86 
1.12 
4.93 
1.20 
2. 98 
4. 00 
1.22 
1.41 
.11 
3.37 
Trace. 
KM). 01 
2.776 
Unfad- 
ing 
green. 
(2) Vt. 
59.37 
1.00 
18.51 
1.18 
6.69 
.49 
2.36 
3.78 
1.71 
.30 
.14 
4.01 
II II Ml.', 
2. 795 
Brigbt 
green. 
(1) 
N. Y. 
67.89 
.49 
11.03 
1.47 
3.81 
1.43 
4.57 
2.82 
.77 
1.89 
.04 
3.21 
KM). 
2.717 
Varie- 
gated 
(Eure- 
ka). (1) 
Vt. 
60.24 
.92 
18.46 
2. 56 
5.18 
.33 
2.33 
4.09 
1.57 
.08 
.16 
3.81 
39 
100. 12 
2. 805 
Pur .P le - Red. 
61.29 
. 77 
16.24 
4.63 
2. 62 
.60 
2.99 
5. 27 
1.38 
.54 
.04 
3. 16 
.56 
(4) 
N.Y. 
63. 89 
.52 
11.80 
4.56 
1.33 
2. 25 
4.57 
3. 95 
.50 
3.15 
.02 
2. 82 
77 
100.09 100.13 
2. 806, 2. 796 
Black. 
(1) 
Vt. 
59. 70 
.79 
16.98 
.52 
4.88 
1.27 
3.23 
3.77 
1.35 
1.40 
1.18 
3.82 
.46 
.70 
1(10.05 
2.774 
Black. 
(1) 
Lebigb 
Co., Pa. 
56. 38 
.78 
15. 27 
ft 1.67 
*>3.23 
4.23 
2.84 
3.51 
1.30 
3.67 
1.72 
4.09 
.59 
1.11 
100.39 
2. 783 
" Figures in parentheses indicate the number of analyses averaged. 
''Approximate. 
If analysis K 2 of red slate on page 73 be included with the four others, the per 
of Fe 2 : , in the red slates would range from 3.48 to 7.10 per cent and would ave 
5.08. Comparing, then, the amount of Fe 2 3 in the colored slates we shall find 
it steadily increases from the variegated to the purple and to the red, as the mi 
scopic sections show. 
On the other hand, there is a decrease of FeO in passing from the unfading g 
to the variegated, sea-green, bright green, purple, and red. This decrease c< 
sponds to and is probably consequent on the decrease of chlorite, a hydrous sili 
of MgO and FeO. 
There is more lime (CaO) and carbon dioxide (C0 2 ) in the Lehigh slate tha: 
any of the others. There is less CaO and C0 2 in the unfading green and in the vj 
gated analyzed than in any of the slates. 
There is less pyrite (FeS 2 ) in the red and most in the black. 
Doctor Hillebrand's discussion of the analyses of New York and Vermont slate 
of the causes of the discoloration of the "sea green " is given on pages 39-42. AV 
that investigation was undertaken primarily to determine the cause of discoloil 
in one kind of slate, microscopic analyses show that discoloration in the black si 
of Pennsylvania is also greatest where carbonate is most abundant. It is saf 
assume that ferrous carbonate plays an important part in the discoloration, not < 
in these slates, but in all slates. The red slates of New York State contain n 
carbonate, but do not discolor, the carbonate probably not being ferrous. 
These 29 analyses are sufficient to give within certain limits the essential chen 
composition of commercial slate of aqueous sedimentary origin. 
Range of co7nj)Osition of slate. 
Silica 
Alumina 
Ferric oxide.. 
Ferrous oxide 
Potash 
Per cent. 
55-67 
11-23 
0. 52-7 
. 46-9 
1. 76-5. 27 
Per 
Soda 0.50- 
Magnesia 88- 
Lime 33- 
Water above 1 10° 2. 82- 
