Emerald
Emeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of connoisseurship: color, clarity, cut and carat weight. Normally, in the grading of colored gemstones, color is by far the most important criterion. However, in the grading of emeralds, clarity is considered a close second. A fine emerald must possess not only a pure verdant green hue as described below, but also a high degree of transparency to be considered a top gemstone. This member of the beryl family ranks among the traditional "big four" gems along with diamonds, rubies and sapphires. Gem-quality beryl and emerald is used in the jewelry trade. Beryl can also be used to as a source of beryllium, a high-strength, lightweight metal with a high resistance to corrosion. Beryllium has a wide variety of applications, including the manufacture of electrical equipment, nuclear reactors, electronic components and aerospace components. The beryllium extracted from beryl crystals at the Triple Chance mine, Broken Hill were used by NASA for the Apollo Space Program.