Formula: (Mg,Fe,Mn)7(Si8O22)(OH,F)2
Reflected/transmitted colour: colourless to pale green
Pleochroism: Mg-rich cummingtonite non-pleochroic, Fe-rich cummingtonite α = β colourless, γ pale green
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.630-1.696, β = 1.644-1.709, γ = 1.652-1.730
Birefringence δ: 0.020-0.045
2Vγ angle: 65-96°
Dispersion: r < v or r > v
Optical orientation: β = y, γ Λ z = 15-21°
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 |