Formula: (Mg,Ca)0.6-0.9(Mg,Fe,Al)6.0[(Si,Al)8O20](OH)4.nH2O
Reflected/transmitted colour: colourless, very pale green or brown
Pleochroism: α paler shades than β and γ
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.520-1.564, β = 1.530-1.583, γ = 1.530-1.583
Birefringence δ: 0.02-0.23
2Vα angle: 0-18°
Dispersion: r ≤ v
Optical orientation: α Λ z = 5-6°, β = y, γ Λ x = 1-2°
Optical axial plane: (010)
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