18 | Pentti Eskola. ER (LXII - 
Lassenose (1, 4, 2, 4), near FOR ORONE 
The Osann fonres 
S Å C FAONKe Ve ji n VR 
73.82. 7:49. 112,32 — 6:50,5-09.0 73:08:05 EEE 
The actual minerals of this rock are plagioclase (about 
Abg0), orthoclase, quartz, green hornblende, titanite, biotite, 
diopside, apatite, magnetite, chlorite and epidote. There are 
many features in the structure and mineral development of 
exceeding interest, and they will (RET TeeR be deseRned in 
some detail. 
At the first sight this rock shows the most bybibalt primary 
consolidation-structure : possible, and every one of the con- 
stituent minerals has its given place in the series of idio- 
morphism. Among the four main constituents the common 
green hornblende is idiomorphic towards all the others showing 
in fact quite an ideal crystalline form, combined of the 
simple forms (110), (001) and (101). Thereafter follows the 
plagioclase, which has a marked zonal structure. Its maxi- 
mum extinction angles in symmetrical sections are about 
5”, but with variable sign in different zones, the percentage 
of albite thus varying from about 75 to 85. Myrmekitiec 
intergrowth of quartz and plagioclase is frequent. The 
largest crystals of plagioclase measure about 2 cm in dia- 
meter, the hornblende prisms averaging 1.5 x 1 x 0.5 cm. 
The interstices between the hornblende and the plagioclase 
are filled up with a mass of orthoclase and quartz. . The 
former shows an idiomorphic development towards the latter 
and forms the very largest crystals in the rock, being, more- 
over, striking by their beautiful salmon-red colour which 
contrasts against the white plagioclase. At places, quartz 
and orthoclase form a micropegmatitic intergrowth around 
crystals of: orthoclase. No microcline is present, neither 
simple nor twinned. | 
Thus the hornblende apparently was the earliest main 
mineral to crystallize out. Strange to tell it is, however, of 
a secondary origin in such a sense that it had originated at 
the expense of other minerals that had crystallized out still 
Kg 
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