262 The Americafi Geologist. November. 1900 
The analysis furnished the values in the first column be- 
low; a series of similar analyses is added for comparison: 
12345 6 789 10 11 
SiOs. 53.38 51.30 54.47 55.59 54.20 53.56 54.00 56.18 54.55 51.89 53.7 
AUOa 29.70 31.46 26.45 25.41 29.10 27.78 27.82 27.33 28.68 29.68 29.6 
FCiOs .21 .... 1.30 2.73 1.10 1.15 .... 1.38 1.03 .32 .... 
FeO 67 1.50 37 . . . . 
MgO. Trace .69 15 Trace .05 38 .... 
CaO 11.90 12.20 10.86 11.40 11.25 12.01 11.20 10.33 11.23 12.62 11.8 
Na^O 4.30 5.53 4.37 4r.83 3.80 4.10 4.76 5.17 4.62 3.87 4.9 
K2O .56 .79 .92 1.32 .... 1.68 .43 .36 .42 .50 .... 
HaO .37 .... .53 40 46 .... 
100.42 101.08 100.20 100.28 100.09 100.28 100.04 1(J0.75 100.53 100.09 100.00 
Sp. Gr. 2.701 2.702 2.72 2.689 2.698 2.700 2.700 2.703 
1. Labradorite separated from the plagioclasyte of Carlton peak, 
Minn, (analyzed by the author). 
2. Labradorite from near Encampment island, Minn. (Analysis by 
W. C. Blasdale, Univ. Calif.: reported by A. C. Lawson: Geol. & 
Nat. Hist. Surv. of Minn. Bull. No. 8, p. 6. 
3. Bluish opalescent labradorite from Mt. Marcy, New York. (A. 
R. Leeds: thirteenth Ann. Rep. N. Y. State Museum Natural History, 
1876). 
4. Labradorite from Paul's island, Labrador: (G. Tschermak in 
Rammelsberg's Mineralchemie). 
5. Blue opalescent labradorite from plagioclasyte of Morin, Can- 
ada (T. S. Hunt: Geology of Canada, 1863). 
6. Bluish-gray untwinned labradorite, Paul's island, Labrador. 
(G. Hawes: Proc. Nat. Museum, Washington, 1881.) 
7. Labradorite, Paul's island, Labrador. With traces of MnO, 
SrO, and LigO; 19 lost on ignition. (Jannasch, Neues Jahrb. f. Min. 
1884.) 
8. Labradorite from Labrador, by C. Clement (Schuster, Mineral, 
u. Petrog. II. 43.) Mitth. Tschermak, Wien, 1880, III, p. 183. 
9. Labradorite from Kamenoi Brod. Kiew, Russia, by Schuster, 
loc. cit., p. 184. 
ID. Labradorite from olivine gabbro, Sec. 35-61-12W., Minn. 
(Analysis by W. H. Hillebrand, U. S. Geol. Surv.; reported by W. S. 
Bayley, Jour. Geol. I, 701, 1893. 
II. Theoretical composition of AbsAn^. 
AuG[TE. While pyroxene may be entirely lacking in some 
thin sections and is never abundant, it is, in small amount, a 
normal constituent of the plagioclasyte. It only rarely shows 
crystal outline, but the facesw(iio), g'{oio), and h''{ioo) have 
been noted. The pyroxenic cleavage is usually very distinct, 
and parting is often developed parallel to h''{ioo) as the augite 
