Formula: (Mg,Fe)Al3(BO4)(SiO4)O
Reflected/transmitted colour:
Pleochroism: dark bluish green (x), colourless (y), dark green (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.602, β = 1.636, γ = 1.639
Bireflectance/Birefringence δ: 0.037
2V angle: 32.2° (calculated), 24-32° (measured)
Dispersion: strong, r < v
Optical orientation:
Optical axial plane:
| 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 |