COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

Suomen Geologinen . eura. N: 0 35. Geologiska Sällskapet i Finland.
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Ouortz
Microclin&
Fig. 8. Variation in the amount of quartz and microcline for the three series of sampIes.
distribution of the porphyroblasts in the rocks. The microcline sometimes
shows Carlsbad twinning, but without preference for any members of the
series.
QUARTZ
The variation in the abundance of this mineral does not display any
particular feature, nor can it be correlated satisfactorily with the variations
in the abundance of other minerals. The quartz shows an allotriomorphic
shape, the recrystallized portion is mostly free from the many little inclusions
(liquid or gaseous) that the quartz otherwise shows. Such inclusions
are often uninterrupted in their alignment through many grains, which means
that they have developed after the formation of such grains. The inclusions
in the quartz sometimes form an alignment constant in the whole section.
The quartz is often fractured and in some cases shows a considerable undulatory
extinction. Drop quartz is found in the altered amphibole. The minerals
contained in the quartz may be biotite, plagioclase and microcline, and
this supports the possible existence, to be discussed later, of several generations
of quartz.
PYROXENE
In each series it is absent in the acid member. In any case, even in
basic ones it has nearly always been partially altered to amphibole, beginning
with pleochroic rims (hornblende, Plate II, Fig. 4) probably owing
to the migration of iron from the co re (introduction of Fe from the outside
and/or removal of lime could have played apart, too), and finally passing
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