Emerald tumbled stones (15-20 mm) from Bahia, Brazil.

Emerald is a variety of beryl and is considered the most precious stone from the beryl group. The colourant is chromium, sometimes vanadium. The chemical formula is Be₃Al₂(SiO₃)₆. Emerald is formed by a combination of intrusive magma and metamorphic transformation of rocks. Deposits therefore occur in pegmatite corridors or in the vicinity thereof. The extraction of crystals takes place almost exclusively from the mother rock, where the emerald has grown in small corridors or on the walls of cavities. Alluvial deposits can hardly form because the specific weight of emerald is comparable to that of quartz. The name emerald can probably be traced back to a Semitic language via Latin and Greek. The Greeks used the name not only for emerald but for various green stones. The emerald has always been considered the 'king of gemstones'. Thousands of years before Christ it was already known and was already mined and used in jewellery, amulets and art objects. Emeralds have been found in the burial chambers of Egyptian pharaohs, in Pompeii and in Herculaneum. Emeralds are also mentioned in the Bible: in the Revelation of John there is mention of a "rainbow that looked like an emerald" around the throne in heaven. Special emeralds are part of treasures and museum collections. Numerous emeralds lie in shipwrecks on the bottom of the seas between America and Europe. The special and striking colour of this gemstone became synonymous with the officially recognised colour emerald green. The name is often used in metaphors for countries. For example, Ireland is also called the Emerald Isle in English because it is so green. Since Multatuli, the Dutch East Indies was known as the Belt of Emerald. In astrology, the emerald is associated with the month of May and the zodiac sign Taurus. In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. The emerald is one of the "nine gemstones" in the Thai Order of the Nine Gemstones.