Zultanite shows color change (the same crystal showing different colors under different illuminants) caused by trace iron and chromium absorbing different wavelengths from each light source. Opal shows play-of-color (rainbow flashes from a single viewing angle) caused by structural diffraction from silica spheres. The two phenomena are visually different and physically unrelated; opal is softer (5.5–6.5 Mohs) and contains water that can desiccate over time.

Mineralogy

Each gem is identified by its mineral species, hardness, refractive index, and optical character. The verified values are documented in the property guides.

Optical phenomenon

The two gems compared here differ in the physics of their optical drama. Color change depends on illuminant; other phenomena depend on structure or viewing angle.

Source and supply

Where each gem is mined and how supply is structured determines availability and price stability.

Jewelry suitability

Hardness, cleavage, and toughness govern which gem suits ring-grade vs occasional-wear jewelry.