Color of Some Gemstones — Important Facts

Important NEET/JEE Facts

1. Ruby: Contains approximately 0.5–1% (Cr3+) ions, which replace some (Al3+) ions in the crystal lattice.
2. Emerald: (Cr3+) ions occupy octahedral sites in the beryl mineral.
3. Both gemstones contain the same color-producing ion, (Cr3+), with a (d3) configuration.
4. Their different colours arise because the crystal environments differ, changing the energies and wavelengths of light absorbed.
5. Ruby appears red because it transmits red light, while absorbing other parts of visible light.
6. Emerald appears green because its absorption bands shift, allowing green light to be transmitted.

Key concept: The color of transition-metal compounds is often due to electronic transitions between crystal-field-split (d) orbitals.