Formula: (K,Na)3(Fe,Mn)7Ti2(Si4O12)2(O,OH,F)7
Reflected/transmitted colour: orange-brown to yellow
Pleochroism: α orange-red (yellow-green), β yellow (yellow-brown), γ lemon yellow (brown
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.676-1.708, β = 1.703-1.738, γ = 1.731-1.747
Birefringence δ: ~ 0.06
2Vγ angle: 60-88°
Dispersion: r > v, strong
Optical orientation: α approximately ┴ (001), β ~ (010), γ ~ x
Optical axial plane:
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