Formula: Ca2(Fe,Mn)FeSi5O14(OH)
Reflected/transmitted green-brown
Pleochroism: a = dark green, b = lilca-green, g = pale to deep brown
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: a = 1.700, b = 1.710, g = 1.725
Birefringence δ: 0.025
2V angle: 50°
Dispersion: r > v, strong
Optical orientation:
Optical axial plane:
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