208 
Analysis of 
essexite-porphyrite. 
20 
STONE te | 50:98 
OP ee | 138 
MO amt 22-15 
FeO, ee | 1:04 
ОЕ | 4°25 
Мао. trace 
Ми. | 119 
Сао еек | 7:90 
Мс. | 6°84 
KO | 271 
H,0 above 110°. . | 1522 
H,O at110° ... | 12 
GR ER AA | trace 
POS | 38 
СО | {гасе 
Total... | 99-76 
Sp. gr.... | 9-89 
20. Essexite-porphyrite, 450 meters above sea-level, Kakarsuak 
near Narsak, 5. Greenland. С. Wintser, analyst. 
twinned and sometimes twinning is wanting. The larger grains 
are often altered in the same way as the phenocrysts. The 
maximum value of the extinclion-angle in sections perpendicu- 
lar to (O10) is 38° in the central part of the crystals. This 
indicates a labradorite of almost the same composition as the 
phenocrysts. The extinction-angle decreases towards the margin 
of the grains and they are surrounded by a zone of orthoclase 
(or soda-orthoclase). This mineral is also found as interstitial 
