Delafossite

Formula: CuFeO2

Reflected/transmitted colour: opaque, polished section light brownish rose

Pleochroism: distinct,  w light golden brown, ε rose-brown

Optical isotropy/anisotropy: uniaxial, polished section very distinct to strong anisotropic, 45° bluish gray, straight extinction, basal sections appear isotropic

Optical sign:

Refractive indices:

Birefringence δ/bireflectance: polished section very distinct, in air w yellowish rose-brown to creamy brown, ε rose-brown, in oil w dull pinkish gray to yellowish gray, ε much darker, cacao-brown to pinkish brown-gray

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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