Formula: BaSr2Mn2O2(Si4O12)
Reflected/transmitted colour:
Pleochroism: Strong, violet to black (X), emerald green (Y=Z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.775, β = 1.792, γ = 1.814
Bireflectance/Birefringence δ: 0.039
2V angle: 84° (calculated), 74-80° (measured)
Dispersion: Strong, r > v
Optical orientation: X = a, Y = b, Z Ù c = 44°
Optical axial plane:
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