Spinel and Black Opal optical properties play a significant role while distinguishing these gemstones from each other. These properties are influenced by the Spinel and Black Opal Physical Properties like crystallographic symmetry, pleochroism,etc. in the crystal. Some of the optical properties are refractive index, luster, optic character, pleochroism etc. Prominent among these is Spinel and Black Opal optic character. You might have noticed your gemologist rotating the gemstone while testing it. Rotating a gemstone along its optic axis helps in determining its optic character.
Similar to their colors, Spinel and Black Opal transparency can also be used as criteria for their primary identification. Although transparency cannot be the only criteria for gemstone identification, it can efficiently used in gemstone grading. Talking about their transparency, Spinel is Translucent, Transparent and Transparent to translucent while Spinel is Translucent, Transparent and Transparent to translucent in appearance.