Formula: Ca2(Mg, Fe)5Si8O22(OH)2
Reflected/transmitted colour: colourless, pale green to deep green
Pleochroism: weak, α = pale yellow, yellowish green, b = pale yellow-green, green, γ = pale green, greenish blue
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.613-1.646, b = 1.624-1.656, γ = 1.636-1.666
Birefringence δ: 0.043-0.053
2V angle: 79-86°
Dispersion: r < v, weak
Optical orientation: b = b, γ Ù c = 14-18.5°
Optical axial plane:
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