Unearthing the dazzle of diamonds (and other gorgeous gemstones).

• Position: Museums Today

VISITORS CAN EXPLORE the natural beauty of Earth's gemstones, along with stunning pieces crafted by artisans, at the renovated Hall of Gems at Chicago s Field Museum, where unusual natural formations, dazzling cut gems, and incomparable jewelry settings are on display, including those of Tiffany & Co. from the 1893 World's Columbian Exposition, exquisite rare stones and gold objects from around the world, and never-before-seen creations from top designers. The gem exhibition has been a favorite destination since it opened in 1921. The Hall was renovated in 1941 and again in 1985. It now showcases displays of 600 gemstones and gems, and 150 pieces of jewelry--and is designed to awe onlookers with a presentation enhanced by state-of-the-art fiber optic fighting.

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'The exhibition combines the beauty of nature with the creativity of human artistry," explains Lance Grande, senior vice president, head of collections and research, and curator of the Hall. "Featured are most of the true major gemstone varieties, including those known for thousands of years as well as some discovered in recent decades. From an Egyptian garnet necklace more than 3,400 years old, to the Aztec Sun God Opal thought to have been mined about 500 years ago, to one-of-a-kind pieces made by leading designers using world-class gems ... the exhibition contains breathtaking pieces from all over the world."

For instance, there is the eye-popping 5,890-carat Chalmers topaz. Not all of the "jewels" are inside exhibition cases, however, as the Hall is graced by a Tiffany stained glass window depicting a mermaid swimming with a goldfish.

All of the gems are arranged according to type, for a greater understanding of their relationships. Each display features a gemstone still embedded in ancient rock, or matrix, in which it was found. Alongside the gemstones in matrix are cut and polished stones, and placed next to those are finished pieces of jewelry. With the gems organized in this way, it is easier to experience the complete story of how a stone is found in its raw state, then cut and polished, and finally transformed into a gorgeous ring, necklace, or brooch worthy of being worn on the red carpet.

The exhibition showcases many gems notable for their size or rarity, including a highly unusual, 11.65-carat color-changing alexandrite that appears emerald green in daylight and then raspberry red in incandescent light, as well as a 97.5-carat ruby topaz and a 341-carat aquamarine.

There is no strict definition of what constitutes a gemstone. It may be a mineral or organic matter that can be cut and polished for jewelry. Once this occurs, it becomes a gem. Beauty, durability, and rarity determine if a material is gem quality.

* Beauty is judged by color and clarity, as well as the way the gem reflects and absorbs light. Cut just right, transparent minerals such as zircon act like prisms to break rays of light into all the colors of the rainbow and exhibit multicolored "fire."

* Durability is desirable because the harder the stone, the less likely it is to scratch or chip. Diamond is by far the hardest gem--it is 140 times more durable than the second-place ruby. Certain softer organic materials, such as pearl and amber, also are considered gem quality.

* Rarity adds to a gem's value--the more difficult to come by, the more precious it becomes, such as ruby topaz. One of the world's largest specimens is on display.

Gemstones are formed over millions of years, yet some have been discovered only in the past century or so. Imagine the excitement felt by mineral collector Thomas Maynard Bixby when, in 1904, he discovered a rare form of red beryl in the mountains of Utah. Today, the gem is called bixbite in honor of him. It is one of the rarest gems in North America and is mined only in Utah. In 1967, Maasi cattle herders came across an unusual blue stone that turned out to be 1,000 times rarer than diamond. Today, we call the gem tanzanite, and it is found only in Tanzania and Kenya. Both bixbite and tanzanite are exhibited.

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Of course, many gems have been known and prized since the dawn of human...