Formula: Al4(Si8O20)(OH)4
Reflected/transmitted colour: colourless
Pleochroism: absorption greater for vibration directions in the (001) plane
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.552-1.556, β = 1.586-1.589, γ = 1.596-1.601
Birefringence δ: ~ 0.050
2Vα angle: 53-62°
Dispersion: r > v, weak
Optical orientation: α Λ z = ~ 10°, β ~ x, γ = y
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 |