28 ARCTIC BASALT PLATEAU 
and corresponds in time to the initial growth of the first generation 
of magnetite; the envelop is relatively free from magnetite inclusions 
and corresponds to the crystallisation of the groundmass-augite. The 
contour of the augite is pointed out by a garland of magnetite, 
melting up together the dentification of the envelop. He forms 
elongated prisms (10 : 1), rarely flattened after (100), and then twinned; 
sometimes the prisms in their parallelism point out a fluctuation 
structure. Extinction angles measured on sections strongly | £, gave: / 
c:7=A47°.s in the distinct core, 
= 48°.5--53°.4 in the intermediate zone, gradual transition, 
= 50°.5 in the outer shell. 
The double refraction, measured with the compensator of Babinet, 
gave 
y—o = 0.023], thickness 0.030 mm., with n= 1.7. 
Axial angle: 2Ey—114°40’, in the intermediate zone 
TOR os Ir athevieGie 
2 V7 — 109° 205 
— (Ol 
Dispersion of axes: A—0o << v strong | 
B—o>v weaker| 
An irregural fissuring of the augite does not allow a measurement 
of the refractive indexes. The dispersion of extinction is considerable 
as tested on different interference tints on both sides of the extinction, 
| calculated for 8 = 1.7 
around 7 
and conformably to the axial dispersion: ey, << :7,. The optical pro- 
perties test an augite perhaps rich in titanium (dispersion!) and lime 
(? double refraction) content, containing soda too (extinction angle!). 
The groundmass is very finely grained and inverted intersertal: 
the narrow and long prisms of augite build up a network, whose 
meshes contain the colourless constituents and partly needles of 
apatite, and whose nodes are represented by olivine individuals. 
In case of diminishing grain, which happens in „Schlieren“, the 
meshes lessen and their content too, the augite prisms growing 
thicker. The magnetite grains are confined along the augite prisms. 
\ 
ie 
