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mica-like substance; where the transformation has progressed 
farther, epidote in rather large crystals also occurs. 
Orthoclase occurs in the fresh specimens of the essexite 
in greatly varying amount, and in some of them it seems to 
be entirely absent. It must be emphasized that even where 
the orthoclase is wanting the mineral composition is for the 
rest unaltered and typically essexitic. In the more decomposed 
varieties of the rock the orthoclase cannot be identified. It is 
always the mineral last crystallized; it partly forms an outer 
covering of the plagioclase crystals and is partly interstitial. In 
the specimens from Sigsardlugtok where it only occurs very 
sparingly it appears to be a normal orthoclase with an angle 
of extinction on (010) of about + 4°. But in the specimens 
from the Islands at Narsak and from Kangerdluak the mineral 
is more abundant and proves to be a soda-orthoclase with an 
angle of extinction on (010) of about + 8°. This soda-ortho- 
clase shows a more or less plain cryptoperthitic striation that 
in sections perpendicular to (O10) follows a direction parallel 
with the b-axis, and in sections parallel with 6 (010) is orien- 
tated under an angle of about + 71° with the a-axis. Il 
is often, but not always, more cloudy than the plagioclase. 
Structure. — As already mentioned the plagioclase in this 
rock is developed in large and rather idiomorphic, tabular cry- 
stals and the dark-coloured minerals fill up the interspaces be- 
tween them. Apatite is always the earliest mineral. After this 
comes iron-ore and olivine. Plagioclase and augite have per- 
haps to a great extent crystallized simultaneously but the cry- 
Stallization of the augite has continued longest and augite- 
anhedra have grown out so that they fill even narrow interstices 
between the plagioclase-crystals. Sometimes also the biotite 
aggregates take part in this filling up of the interstices. When 
orthoclase is present it is of even later date than the augite. 
Usually each anhedron of augite fills only one interstice and in 
no place the augite-anhedra are large enough to mould several 
