Formula: (Fe, Mg, Zn)2(Al,Fe,Ti)9O6[(Si,Al)O4]4(O,OH)2
Reflected/transmitted colour: pale golden yellow
Pleochroism: α colourless, β pale yellow, γ golden yellow
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.736-1.747, β = 1.742-1.753, γ = 1.748-1.761
Birefringence δ: 0.011-0.014
2Vγ angle: 80-90°
Dispersion: r > v, weak
Optical orientation: α = y, β = x, γ = z
Optical axial plane: (100)
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