Formula: (Ba,K)(Mg,Mn,Al)3Si2Al2O10(OH)2
Reflected/transmitted colour:
Pleochroism: Very light yellow (x), light brownish yellow (y), light brownish yellow (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: a=1.619, b=1.628-1.633, g=1.635
Bireflectance/Birefringence δ: 0.016
2V angle: 40-82° (calculated), 23° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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