COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

Suomeu Geologiueu Seura. N:o 35. Geologiska Sällskapet i }'inlund. 33
The calcium content of the mineral is considerably lower than that of
the juddite from Chikla and lower than observed in most arfvedsonites. The
low lime content is, however, in accordance with the ideal end member
formula proposed for the arfvedsonite-eckermannite series by Sundius
(1945).
THE GOLDONGRI MANGANE SE MINE, PANCHMAHAL DISTRICT,
GUJARAT STATE
The Goldongri is a small isolated hill which rises to ab out 60 m from
the surface level and is 90 m long and nearly 60 m wide. The only work
conserning it in the literature is one by the late Fermor (1909), who visited
the pI ace in 1902 and described its geology, mineralogy and petrography to
so me extent. The ore-body is intricately folded and an interesting variety
of minerals occurs here in the contact between the manganese ore and the
pegmatite and granite intIUsions.
During the years 1957- 1959, one of the authors (V. K. N.) visited the
Goldongri Mines and collected several interesting mineral sampIes for investigation.
The present paper records the studies on eckermannite and
piemontite.
ECKERMANNITE
This alkali amphibole occurs in Goldongri as grains 1 mm in diameter in
an even-grained rock with quartz, microcline, oligoclase, apatite, biotite and
aegirinic pyroxene. The mineral is characterized by astrange colour, which
varies, in thin sections, from violet to light blue.
The purified mineral was chemically analysed. The analysis is given in
Table 6. The unit cell conte nt and the calculated formula agree well with
the ideal formula of the eckermannite-arfvedsonite series suggested by
Sundius (1945): Naa{Mg, Fe+ 2 )4{Fe+ a , Al)SisOsOzz{OH,F}z. Some of the
tri valent iron is replaced by Mn+ 3 in the analysed mineral. The magnesium
content of the mineral is very high and the Mg to (Mg+Fe+Mn)
ratio puts the mineral into the eckermannite end of this series. Optically,
the mineral now under consideration is similar to the ecker mannite mineral
originally described by Adamson (1942, 1944) from Norra Kärr, Sweden.
The optical properties are given in Table 7. The main difference is observed
in the angle of extinction and in the pleochroism. The difference in colour
is evidently associated with the manganese content of the Indian mineral.
The manganese percentage of this mineral, however, is considerably lower
than that of the manganarfvedsonite described above.
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