Allophane

Formula:  Amorphous Al2O3.1.3-2.0(SiO2).2.5-3(H2O) 

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: isotropic

Optical sign:

Refractive indices: n = 1.468-1.512 (air-dried)

Birefringence δ:

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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