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Gifts from the Earth: Emeralds

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Beryl
Be₃Al₂Si₆O₁₈;
Beryllium Aluminum Silicate

Beryllium is another rare and very hard mineral that forms in several different ways:

1) Some beryl deposits have been found in rocks of intrusive, igneous origins, such as cavities within granite and pegmatite. Beautiful red beryl crystals have also been found in extrusive, volcanic deposits.

2) Other forms of beryl have also been found in metamorphic rocks where the basic elements that form beryl (beryllium, aluminum, and silicates) leach out of intruding granite that pass into the adjacent, silica-poor rock formations where they crystallize.

3) Greisens are another type of rock in which beryl may be found. Greisens are formed when extremely hot, mineralized water passes through fractures and cracks in granitic rock. This superheated mineral water alters the granite host rock in a process known as hydrothermal alteration.

In its purest natural (uncut) form, this mineral forms long, hexagonal prisms and is known as goshenite. It also comes in a variety of colors, depending upon the mineral impurities that have entered the crystal during its formation. Unlike sapphires, several different colors of the mineral beryl are separately classified gemstones. Some of the lesser known variants of the mineral beryl are; heliodor (yellow), morganite (pink), aquamarine (pale blue-green), but the best known, most highly valuable variant of beryl is the deep green emerald...

Emeralds

The element that gives emeralds their beautiful green color is the same element that turns corundum into red rubies - chromium. The base mineral composition of rubies differs from that of emeralds (Al₂O₃ for rubies, Be₃Al₂Si₆O₁₈ for emeralds) so the chromium trapped within the crystal lattice of each absorbs different colors of the visible spectrum of light; the chromium in rubies reflect red and the chromium in emeralds reflect green.

Unlike other precious gemstones, impurities, inclusions (gas bubbles and other minerals), small fractures, and other intrusions into emerald crystals do not detract from the value of a stone. On the contrary, the minor imperfections found deep in the interior of a transparent, natural emerald are what give it "character" and assure the owner that is truly unique, original and unaltered stone.

The largest uncut emerald was found in Carnaiba, Brazil in 1974. It was an incredible 86,136-carat natural beryl crystal. The stone was eventually valued at $1,120,080 USD. The largest emerald crystal ever discovered was 7,025 carats and was found in a mine in Colombia.