COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

62 Bulletin de la Co=ission geologique de Finlande N: 0 212.
Fig.4. Porphyroblast of perthitic orthoclase. Granodiorite (42/JP/62. Fig. 1.
area I). N +. magn. 40 x .
quarried for a short while to produce stones used during the building of
the railway from Haapamäki to Pori. The first sam pIe taken from this
quarry contains large, pinkish gray porphyroblasts of potash feldspar,
which have a triclinicity of 0.85 (50/JP/62, Table 3). Later on, three more
sampIes were collected from different parts of the same quarry, and they
have the following values of triclinicity:
33-1/KH/62: Mainly 0.9, small part 0.0
33-2/KH/62: 0.0-0.8, no max.
33-3/KH/62: 0.0-0.75, max. at 0.75
This test also supports the view that within an area like that of map
sheet 2232, where low triclinicities are conspicuously widespread, true,
homogeneous microcline porphyroblasts are uncommon and probably occur
patch-wise. Concerning the latekinematic granites of the same area, on the
other hand, microcline is the only modification of potash feldspar so far
met with.
There is no sense in describing petrologically and mineralogically all the
rocks examined and listed in Tables 2 and 3, the rock types of the area
having been described by Marmo (1963). As examples, however. the following
very brief type descriptions will be given.
SampIes 301 and 355/MT/61 (Table 2), porphyroblastic granodiorite,
contain insets of sericitic plagioclase with 27 % An (measured using the