Formula: K2(Mg,Fe)6-4(Fe,Al,Ti)0-2(Si6-5Al2-3O20)(OH,F)4
Reflected/transmitted colour: pale yellow or pale green to yellow, green or brown, lighter than biotite
Pleochroism: α yellow, grayish yellow, brownish green, brown, β = γ brownish red, yellow, green, dark green, dark reddish brown, dark brown
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.530-1.625, β = 1.557-1.696, γ = 1.558-1.969
Birefringence δ: 0.028-0.08
2Vα angle: 0-25°
Dispersion: r < v, weak
Optical orientation: β = y, γ Λ x = 0-9°
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 |