Formula: Mg2Al(SiAl)O5(OH)4
Reflected/transmitted colour: colourless
Pleochroism:
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: a = 1.597, b = 1.599, g = 1.615
Birefringence δ: 0.018
2V angle: 18°
Dispersion: r < v
Optical orientation:
Optical axial plane:
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