Formula: Na2Fe5TiO2(Si6O18)
Reflected/transmitted colour: reddish brown to black
Pleochroism: α light yellow brown, reddish brown, β reddish to dark brown, γ deep reddish brown, brownish black to opaque
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α =1.790-1.810, β = 1.805-1.826, γ = 1.870-1.900
Birefringence δ: 0.070-0.080
2Vγ angle: 27-55°
Dispersion: r < v, very strong
Optical orientation: γ Λ z = 40-45°
Optical axial plane: ~ (010)
| Back to Alphabetical list | Colour photos | Physical, chemical and crystallographic description | SEM images | TEM images | vibrational spectra description | IR spectra | Raman spectra | N-IR spectra | F-IR spectra | IES spectra |