Formula: CaMn6Si3O16 . 7H2O
Reflected/transmitted colour: red- to yellow-brown
Pleochroism: strong, a = b = red-brown, g = yellow-brown
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: a = 1.775, b = 1.798, g = 1.800
Birefringence δ: 0.025
2V angle: 25°
Dispersion: r < v, strong
Optical orientation:
Optical axial plane:
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