MINERAL: Beryl CHEMISTRY: Be3Al2Si6O18 COLOR: Vibrant green
REFRACTIVE INDEX: 1.577 to 1.583 BIREFRINGENCE: 0.005 to 0.009
SPECIFIC GRAVITY: 2.72 MOHS HARDNESS: 7.5 to 8
The most valued variety of beryl, emerald was once cherished by Spanish conquistadors, Inca kings, Moguls, and pharaohs. The first known emerald mines were in Egypt, dating from at least 330 BC into the 1700s. Cleopatra was known to have a passion for emerald, and used it in her royal adornments. Today, fine gems come from Africa, South America, and Central Asia.
Emerald is the bluish green to green variety of beryl, a mineral species that includes aquamarine. There are other green gems, like tourmaline and peridot, but emerald is the one that’s always associated with the lushest landscapes and the richest greens. Its color reflects new spring growth, which makes it the perfect choice of a birthstone for the month of May. It’s also the gemstone for twentieth and thirty-fifth wedding anniversaries.
MINERAL: Corundum CHEMISTRY: Al2O3 COLOR: Every color but red REFRACTIVE INDEX: 1.762 to 1.770 BIREFRINGENCE: 0.008 to 0.010
SPECIFIC GRAVITY: 4.00 MOHS HARDNESS: 9
Traditionally, sapphire symbolizes nobility, truth, sincerity, and faithfulness. It has decorated the robes of royalty and clergy members for centuries. Its extraordinary color is the standard against which other blue gems—from topaz to tanzanite—are measured. In folklore, history, art, and consumer awareness, sapphire has always been associated with the color blue. Its name comes from the Greek word sappheiros which means “blue stone”.
Blue sapphire belongs to the mineral species corundum. It can be a pure blue but ranges from greenish blue to violetish blue. Besides blue sapphire and ruby, the corundum family also includes so-called “fancy sapphires.” They come in violet, green, yellow, orange, pink, purple, and intermediate hues. Some sapphires can also exhibit the phenomenon known as color change.
MINERAL: Corundum CHEMICAL COMPOSITION: Al2O3 COLOR: Red
REFRACTIVE INDEX: 1.762 to 1.770 BIREFRINGENCE: 0.008 to 0.010
SPECIFIC GRAVITY: 4.00 (+/- 0.05) MOHS HARDNESS: 9
Traces of chromium give this red variety of the mineral corundum its rich color. Long valued by humans of many cultures, the name ruby comes from the Latin word ruber, which means “red.” In ancient Sanskrit, ruby was called ratnaraj, or “king of precious stones.”
Ruby is the most valuable variety of the corundum mineral species, which also includes sapphire. Rubies can command the highest per-carat price of any colored stone. This makes ruby one of the most important gems in the colored stone market.
Ruby is the birthstone for July and the gem for the 15th and 40th anniversaries.
MINERAL: Diamond CHEMISTRY: C COLOR: Colorless
REFRACTIVE INDEX: 2.42 BIREFRINGENCE: None
SPECIFIC GRAVITY: 3.52 (+/-0.01) MOHS HARDNESS: 10
Diamonds are among nature’s most precious and beautiful creations.This hardest gem of all is made of just one element: carbon. It’s valued for its colorless nature and purity. Most diamonds are primeval—over a billion years old—and form deep within the earth.
Diamond is the only gem made of a single element: It is typically about 99.95 percent carbon. The other 0.05 percent can include one or more trace elements, which are atoms that aren’t part of the diamond’s essential chemistry.
Diamond is recognized today as the birthstone for April. Diamond is also the gem that marks the 60th and 75th wedding anniversaries.