Formula: (Mn,Ca)4(Al,Mn)5Mg(SiO4)2(Si3O10)(As,V)O4(OH)6
Reflected/transmitted colour: yellow to brown
Pleochroism: strong, a = dark brownish yellow, b = golden yellow, g = pale yellow
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: a = n.d., b = 1.74-1.78, g = n.d.
Birefringence δ: 0.15-0.20
2V angle: 0-70°
Dispersion:
Optical orientation: g = b or c
Optical axial plane:
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