30 ARCTIC BASALT PLATEAU 
strong birefraction of the starting mineral to completely dull pseudo- 
morphs of iron oxide, due to late overheating of the outer parts of 
lava by escaping steam and gas masses during the eruption. — The 
vesicles are empty. 
An incidental estimation by the Rosiwal method of the mineral com- 
position of the darker dense rock by volume is tabulated as follows: 
Minerals: Volume %o: 
IAD ATER OC ian SE Za 
Maenente and peroiskites =: san. aes 6.0 
Golonrless minerals. 2 en 44.5 
Olivinerand.ausiter ke. oe ei ce 47.4 
100.00 
This rock was analysed by Dr.N.Sahlbom with the following results: 
9 A Molecular Di Figures 
SHE Mineral composition („Norm“) of Osann 
bers | cent. 
SiO, 41.18 | 44.66 | 0.686 | 45.72| Ne............ a L. 37.48 | 5 °° 45.7 
Al,O, 169i 1297. ,0:115.) 7.23 |, Ze se ek EEE NEG ANSE 
PeO d.41 | 3.84 | 0.034). — Se a7 ke Cee 010 
FeO 7.94 | 7.55 | 0.110 |f11.50 Pye 39g 
MgO 10.58 | 9.35 | 0.265 | 16.63 CaSiO, ... 8.00 Ih sia ty TE 
CaO oes 8.82 ou 10.87 | Di MgSiO, ... bal pois are 
Na,O 0.88 | 4.24 | 0.095 | 5.99 FesiO; se) ai C22 O20 
K,O 8208: 15 72278: |. 0:033112.06.| Aine Ge sera N 6.01 I O9 
H,O at 110” | 0.11 | 048] — | — R...:0.5 
HO>110°| 0.17} 0.8| — | — Ol eo . . 14.70 M ..12.s1 
co, none|none| —# — Besıo, 7 Saf O. .29.33 | M’.. 0.82 
TiO, 2.34. 2:76 | 50.029')<° — | Am ne ee: 9.43 
RIO 1.25 | 1.10 | 0.009 | — 
Cr,O, Day ee ee (ARN RN ee 08 
MnO oe MESSER ee 4.87 
NiO none) 0.26; — AR Aura. 27 A 
BaO 7 se ONE = fem 62.66 
99.65 | 99.71 100.00 100.34 
Spec. gr. | 3.045) — Magmatic symbol: 
TVG 2 OG 2 aaldose 
Ill, 9, 1, 4 Jivaarose1 
1 The ratio sal: fem lies strictly on the limit between class III and IV; in both 
subdivisions of these classes nephelite basalts are richly represented. 
