June Birthstone: Lovely Pearls

Pearls have been a passion and even an obsession of people throughout the ages.  They have been ground up and used in cosmetics and as a medicine to treat heart and stomach conditions.  Some cultures swear by pearls as an aphrodisiac. These gems have adorned crowns, clothing, and temples, and were said to be a favorite of Cleopatra.

Only those with royal status once wore pearl jewelry, but eventually these gems were seen among all classes of people.  They continue to be viewed as a mark of taste and refinement as well as a symbol of purity, and they are often given to celebrate a marriage or the birth of a child.  Pearls are nature's perfect gift, suitable for all ages, and elegantly worn with everything from jeans to an evening gown.

When impurities are added to colorless gemstones, brilliant colors are frequently produced. When chromium is added to colorless corundum, a red ruby is born, and a green emerald emerges when chromium is added to colorless beryl. Diamonds can be colored blue or yellow by the addition of impurities. Amethyst's violet tint is the result of iron impurities in crystalline quartz, although this impurity acts differently than the chromium impurity that produces the red color of ruby.

Many gemstones' distinctive colors come from the presence of transition metals as impurities in an otherwise transparent crystal lattice. This can be because of a so-called crystal-field or, alternatively, a ligand-field effect. In this crystal field or ligand field effect, the field exerted by the host crystal on the guest impurity fixes the energy levels of the latter as a photon absorber. Put another way, the chemical bonding between the host crystal and guest impurity always involves the donation of electrons from the host crystal to empty energy levels in the metal impurity, binding the metal to the crystal.