Formula: Ca4Be2Al2Si9O26(OH)2
Reflected/transmitted colour: colourless
Pleochroism:
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: a = 1.578-1.586, b = 1.579-1.585, g = 1.583-1.593
Birefringence δ: 0.0-0.015
2V angle: 22-58°
Dispersion:
Optical orientation: a = c, b = b, g = a
Optical axial plane:
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