Formula: (Na,K)2PbAs4(Ta,Nb,Ti)4O18
Reflected/transmitted colour:
Pleochroism: Pale yellow (x), light reddish brown (y), reddish brown (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: a = 2.1
Bireflectance/Birefringence δ:
2V angle: 80 (measured)
Dispersion: Very strong r < v
Optical orientation:
Optical axial plane:
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