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Suomen Geologinen Seura. N: 0 35. Geologiska Sällskapet i Finland. 91
From Isojärvi, in the parish of Oulainen, Wilkman (1931) describeds an
unakite porphyry of fluidal structure. The phenocrysts consist of dark red
pure albite (1.5222 < a :s:: 1.526).
From Ollikkaanvuori, NE Haapavesi, Wilkman describes an unakite
(with analysis) which contains slightly more microcline than albite and less
than the usual amount of epidote (6 %). The double refraction of the epidote
is given as 0.037, corresponding to a Fe 2
0 3
content of 27 %.
From Naistenkallio, near Vatjusjärvi in the commune of Haapavesi, he
describes a small-grained unakite which is traversed by porphyric unakite
veins. This equigranular unakite (analysis) contains 38.7 % albite, 37.7 %
epidote and 15 % microcline. The chlorite of these occurrences is green
and the quantity is from 1.5 % and 2.4 % to 4.4 %.
Wilkman (1938) describes several unakite occurrences from the Kuopio
section characterized by comparatively strong pleochroism of the chlorites
(yellowish to grass-green).
Besides these descriptions accompanying the section maps, Wilkman
(1928) has published a small monograph on the unakites, in which he deals
with occurrences in the N orth Bothnian coastal districts.
Mäkinen (1916) has, as mentioned, also described the unakites from the
district of North Ostrobothnia under the name of natron syenites and kalinatron
syenites. He emphasizes that they are hypidiomorphic abyssal
rocks and gives two analyses, included in Table 1 shown on p. 92, pointing
out that their high sodium and aluminium content depends on the high
albite content, and, further , that they contain no anorthite, but that the
lime, corresponding to 15-25 % normative anorthite, is not contained in
anorthite or plagioclase, instead of which the CaO is almost entirely contained
in the epidote.
The present author would in this connection like to point out that the
typical sodium unakites are not only free from anorthite but also from biotite,
and mostly also from hornblende. All t h e pot a s h g 0 e s i n tot h e
m i c r 0 c 1 i n e a n d n 0 bio t i t eis f 0 r m e d, a n d a 11 t h e
I i m eis c 0 n t a i n e d i n t h e e p i d 0 t e, n 0 a n 0 r t hit e bei n g
f 0 r m e d. It should also be pointed out that one might expect the formation
of anorthite in a magma of the composition of the unakite magma.
But in this case no anorthite is formed, while the calcium of the magma,
combined with water, enters into a chlorite andjor a serpentine molecule.
As seen from the publications on unakites cited, there are about 30 to
40 unakite occurrences in the NW part of Central Finland. A great many
of them lie inside the zone mentioned in the description of the hypersthene
granites, but only in the NW part of this belt, most of them in Oulainen,
Haapajoki and Haapajärvi, the easternmost occurrences being those situated
about 30 km SE of Suonenjoki and ab out 50 km SW of Kuopio and at