Formula: Ba4(Ti,Fe,Fe,Mg)4(B2Si8O27)O2Cl8
Reflected/transmitted colour:
Pleochroism: Strong, yellow-brown (X=Y), opaque (Z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.739-1.753, β = 1.749-1.761, γ = 1.77-1.782
Bireflectance/Birefringence δ: 0.029-0.031
2V angle: 64-70° (calculated), 45-77° (measured)
Dispersion:
Optical orientation: X = c, Y = b, Z = a
Optical axial plane:
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