Formula: (Ca,Mn,Ce,La,Y,Th)2(Fe,Fe,Ti)(Al,Fe)2O.OH(Si2O7)(SiO4)
Reflected/transmitted colour: occasionally colourless but usually brownish yellow or brown
Pleochroism: α reddish brown, β brownish yellow, γ greenish brown to brownish red, reddish brown and dark reddish brown
Optical isotropy/anisotropy: biaxial
Optical sign: +,-
Refractive indices: α = 1.690-1.813, β = 1.700-1.857, γ = 1.706-1.891
Birefringence δ: 0.013-0.036
2Vα angle: 40-123°
Dispersion: r > v, moderate-strong
Optical orientation: α Λ z = 1-42°, β = y
Optical axial plane: (010)
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