Akrochordite

Formula: Mn4Mg(AsO4)2(OH)4.4H2O

Reflected/transmitted colour: colourless to faint pink

Pleochroism:

Optical isotropy/anisotropy: biaxial

Optical sign: +

Refractive indices: α = 1.672, β = 1.676, γ = 1.683

Birefringence δ: 0.011

2V angle: medium

Dispersion: r < v, moderately strong

Optical orientation: α = b, γ ^ c = ~45°

Optical axial plane:

 

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