Reference work entry
Emerald is also called Luzon Green or ‘Green Gemstone’ in Chinese. Emerald is a bright green translucent beryl, the composition of which is a silicate of beryllium and aluminium. It has a glassy lustre and a Mohs hardness of 7.5. It is hard but brittle and easy to crush. Its interior often has wool-like inclusions similar to those of quartz crystals. These inclusions are commonly known as bagasse or cicada wings, which are important features for the identification of natural emeralds. Top-grade emeralds should be pure, bright green and transparent without impurities. Stones larger than 2 carats are rare. Emerald has the name ‘King of the Green’ and is one of the world’s four precious gems along with diamonds, rubies and sapphires. Gem-grade emeralds usually form in pneumatolytic hydrothermal environments and become placer deposits after weathering. The world’s leading mining countries include Colombia, Brazil and Russia (Fig. 5).
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