Tanohataite, LiMn
2Si
3O
8(OH), the Li analogue of serandite, has been found in a metamorphosed manganese ore deposit of the Tanohata mine, Iwate Prefecture, Japan. The mineral has the triclinic space group
P1 with
a = 7.612(7),
b = 7.038(4),
c = 6.700(4) Å,
α = 90.23(6)°,
β = 94.70(7)°,
γ = 105.26 (8)°,
V =345.0(3) Å
3, and
Z = 2. The seven strongest lines in the X-ray powder diffraction pattern are [
d(Å), (
I), (
hkl)]: 6.64(35)(001), 3.67(26)(200), 3.13(89)(102), 3.11(69)(211), 2.95(100)(102), 2.81(33)(120), and 2.18(40)(103). Electron microprobe analysis and laser ablation microprobe-inductively coupled plasma-mass spectrometry gave an SiO
2 content of 51.97; MnO, 37.99; MgO, 1.06; CaO, 0.41; Na
2O, 1.97; Li
2O, 3.34; total, 96.74 wt%, corresponding to an empirical formula of (Li
0.78Na
0.22)
Σ1.00(Mn
1.86Ca
0.03Mg
0.09)
Σ1.98Si
3.01O
8(OH) on the basis of O = 9. Tanohataite is transparent and pinkish white with a vitreous and silky luster. The streak is white. The cleavage is perfect on {001} and {100}. On the Mohs' scale, the hardness is 5-5
1/
2. The calculated density is 3.33 g/cm
3. Optically, tanohataite is biaxial positive with 2
Vcalc = 82(2)°,
α = 1.593(3),
β = 1.618(3), and
γ = 1.653(3). Tanohataite occurs as an aggregation of fibrous crystals in veinlets composed mainly of quartz, aegirine, Mn-arfvedsonite, nambulite, natronambulite, and barite.
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