Formula: Cu2O
Reflected/transmitted colour: cochineal red or red in thick sections, thinner sections yellow-orange, yellow, lemon-yellow, polished section gray with bluish tint, commonly and characteristically with deep red internal reflections
Pleochroism: anomalous (common)
Optical isotropy/anisotropy: isotropic (sometime anomalous anisotropic), polished section always shows strong anomalous anisotropy, deep gray-blue to olive-green. Due to the abundant internal reflections better visible in air than in oil
Optical sign:
Refractive indices: n = 2.849
Birefringence δ/bireflectance: polished section bireflectance visible on close examination
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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