COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

Suomen Geologinen Seura. N:o 35. Geologiska Sällskapet i Finland. 31
The symmetry and the unit cell dimensions were determined with the
single crystal Weissenberg method. The values obtained were checked ~y
calibrated powder photograph measurements (Table 3). The indices of the
d-lines and the refinement of the cell dimensions were obtained with the
aid of the Wegematic 1 000 electronic computor. MI'. Törn, M. Sc., of the
Computing Centre in Turku, drew up the program for computation.
Table 1 shows that the mineral is very rich in sodium and in ferric iron.
The aegirine content must thus be high in the mineral analysed. This fact
is also observed in the optical properties of the mineral. For comparison,
optical values reported for blanfordite by Fermor (1909), Bilgrami (1956),
Zwaan and van Plas (1958), and Kilpady (1960) are reproduced in Table 2.
The refractive indices of blanfordite from Chikla are considerably lower
than those measured on our mineral. This is in fair accordance with the
higher aegirine content of the now analysed mineral. The values measured
on the blanfordite from Nagpur by Zwaan and van der Plas (ap. cit.)
indicate a still higher aegirine solid solution in the mineral. The now analysed
mineral is, according to the optical properties highly similar to the
variaties studied by Fermor (1909) and by Kilpady (1960).
The single crystal X-ray photographs show systematic extinctions in
agreement with the space group C 2/c. The cell dimensions do not greatly
differ from the values measured for the pure aegirine end member by Yagi
(1958). The smaIl manganese content in the mineral does not greatly affect
the cell size. Its peculiar pleochroim is the only property of the mineral
that readily shows the manganese content.
MANGANARFVEDSONITE (JUDDITE)
This amphibole mineral occurs as small, 1- 2 mm grains together with
blanfordite in an even-grained, banded microcline gneiss. The mineral has
a beautiful pink colour and a strong pleochroism from light rose to violet.
After separation in Clerici's solution, the mineral was chemically analysed
and investigated optically as weH as with X-rays, using powder and single
crystal methods.
The chemical composition of the mineral is shown in Table 4; together
with the calculated atomic content of the unit cello The optics of the mineral
are illustrated in Fig. 1 and the numerical values given in Table 5.
The powder data of the mineral are listed in Table 3. The d-lines are
indexed by means of the cell dimensions obtained on the Weissenberg photographs.
The analysed mineral can be classified as belonging to the eckermannitearfvedsonite
series. The ratio Mg: (Mg+Fe+Mn) = 0. 55 indicates that the
mineral should be called magnesioarfvedsonite, after the nomenclature