Final answer:
The color of gemstones such as rubies and emeralds is determined by the substitution of Al³+ ions with Cr³+ ions in different host lattices, influencing d orbital-ligand interactions and light absorption. Treatments to improve gemstone appearances may not always be disclosed, leading to asymmetric information in the marketplace.
Step-by-step explanation:
The color of gemstones is a fascinating topic that bridges the gap between chemistry and the beauty of gemstones. For example, when Al³+ ions in the crystal lattice of corundum are replaced by Cr³+ ions, the result is a red ruby. This is because the Cr-O distances in ruby are short due to the constraints of the Al2O3 host lattice, which intensifies the d orbital-ligand interactions leading to the absorption of green light and the transmission of red light. Conversely, in emeralds, replacing Al³+ with Cr³+ in beryl's host lattice, Be3Al2Si6O18, the Cr-O distances are longer. This lattice includes large [Si6O18]¹²- silicate rings causing decreased interactions and a smaller Ao, resulting in the absorption of red light and the transmission of the characteristic green color of the emerald.
Additionally, treatments such as oiling or the use of epoxy can be used to enhance the appearance of emeralds, which can lead to issues of asymmetric information in the market, where sellers may not disclose such treatments to the buyers, making it crucial for consumers to be aware and cautious when purchasing gemstones.