Yoshimuraite, a new barium-titanium-manganese complex silicate mineral, was found in an alkali-pegmatitic facies bordering the bedded manganese deposit of the Misago ore body of the Noda-Tamagawa mine. Yoshimuraite occurs as dark-brownish platy to tabular crystals, or sometimes in the stellate groups embedded in coarse aggregates of barium-bearing potashfeldspar, quartz, richterite, urbanite, rhodonite etc.
It resembles lamprophyllite and astrophyllite which usually occur in alkali-pegmatites. It is orange brown in colour, brittle and has a perfect cleavage parallel to {010} and distinct cleavages on {10
?? } and {101}. Polysynthetic twinning on {010} is common. Hardness, 41/2; Sp. gr., 4.13 (obs.) and 4.21 (calc.). Triclinic, with
a0=7.00,
b0=14.71,
c0=5.39Å, α=93.5°, β=90.2°, γ=95.3°, and
a:
b:
c=0.476:1:0.366. Space group, P
?? . Biaxial positive with α=1.763, β=1.777, γ=1.785, (+)2
V=85°-90° ρ〉υ, and absorption X〈Y ?? Z. Optical orientation, γ′ nearly parallel to c-axis, α′ nearly parallel to a-axis. Pleochroism, α bright yellow, β orange-brown, γ brown.
Chemical analysis by J. Ito gave SiO
2 18.25, TiO
2 10.00, Fe
2O
3 1.32, FeO 1.47, MnO 17.64, MgO 0.56, ZnO 0.50, BaO 33.51, SrO 4.62, Na
2O 0.16, K
2O 0.03, P
2O
5 3.98, SO
3 5.40, Cl 0.41, H
2O(±) 2.34, less for Cl 0.09, total 100.10%. The results indicate a formula of approximately X
2Y
2 (Ti, Fe) O (Si
2O
7) ?? (P, S)O
4 ?? (OH) or X
2Y
2 (Ti, Fe) (SiO
4)
2 ?? (P, S)O
4 ?? (OH), where X=Ba, Sr and Na, Y=Mn, Fe, Mg and Zn.
The mineral is named after Professor Toyofumi Yoshimura who has contributed much to the study of manganese minerals in Japan.
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