COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

28 Bulletin de la Commission geologique de Finlande N: 0 212.
1909) are classical in this respect. The four minerals described in this paper
originate from a collection of rock sampies from Indian manganese deposits
which one of us (V. K. N.) sent to the mineralogical museum of the newly
established Institute of Geology of the University of Turku, Finland. The
authors, as far apart geographically as they are, have a common interest in
manganese silicates and the minerals now under consideration were so
beautiful and showed such a remarkble pleochroism that they simply not
could be left unstudied.
NORTH TIRODI MINE, BALAGHAT DISTRICT, MADHYA PRADESH
The Tirodi Mine is the type locality for the alkali amphibole tirodite.
The specimen now studied was collected by Mr. D. K. Chatterjee, geologist
of the C. P. M. O. Co., Ltd. It comes from pit No. 34 of the mine and it
occurred in association with a pegmatite body in contact with the ore zone.
BLANFORDITE
The mineral blanfordite, a manganiferous pyroxene from the Kacharwahi
manganese mine in the Nagpur district, was originally discovered and
named .by Fermor (1906) after W. T. Blandford. Subsequently, similar
pyroxenes were reported by him (1909) from four different Indian localities.
Although Fermor did not know whether all these minerals were the same
as the Kacharwahi pyroxene, he nevertheless included them tentatively
under the term blandfordite. Krishnan (1937) reported a blanfordite type
of pyroxene from Gangpur State, India. In re cent years reports of the
mineral have co me from the Ponia and Tirodi manganese mines in the
Balaghat district (Kilpady and Dave 1958), from Chikla in the Bhandara
district (Bilgrami 1956) and from the Nagpur district (Zwaan and van der
Plas 1958).
In the North Tirodi mine, blanfordite occurs as anhedral, I-mm crystals
in a granular banded rock together with microcline, manganarfvedsonite
(juddite), mangan-chlorite and braunite.
The mineral was purified using Clerici's solution and analysed. The
chemical analysis was performed by Mr. Paavo Väänänen, M. Sc., of the
Geological Survey of Finland. The composition of the mineral is given in
Table 1. The table also lists the unit cell dimensions and the cell content of
the mineral. The content of the unit cell is calculated on the basis of the
chemie al analysis, the cell dimensions given and the specific gravity measured.
The optical properties and the orientation of the mineral are given in
Table 2 and in Fig. 1.