The German word for glasses, Brille, comes from beryl, the mineral behind emeralds
When 13th-century Italians made the first spectacles, ordinary glass was too cloudy, so lenses were ground from beryl or rock crystal. That is why Germans still call glasses Brille. The same mineral, pure and colourless by nature, becomes emerald, aquamarine or rare red gems when stray atoms slip into its crystal.
Beryl is a beryllium aluminium silicate and the main ore of beryllium. Its name travelled from Greek through Latin and Old French, and probably began in a Dravidian place name, perhaps the town of Belur or Velur in Karnataka. Chemically it is a ring silicate: stacked rings of silicon and oxygen form columns with open channels running through the hexagonal crystal. Those channels can hold assorted ions, atoms and molecules, which upsets the crystal's charge balance and invites further swaps, and that is where its colours come from.
Each colour has a chemical signature. Emerald is green beryl tinted by around 2% chromium, sometimes vanadium, and is usually riddled with inclusions that make it fragile; Colombian stones from belts such as Muzo and Chivor are the most prized, and rare trapiche emeralds carry a six-spoked star of dark carbon. Aquamarine's pale blue comes from iron in one form, golden beryl's yellow from iron in another, and morganite's pink from manganese. Colourless goshenite, named after Goshen in Massachusetts, was once used for lenses. Red beryl, the rarest variety, is known from only a handful of North American sites, and most gem-quality material comes from a Utah claim found in 1958 by a man prospecting for uranium.
The mineral is widespread, especially in granitic pegmatites, and its crystals can be colossal. One from Albany, Maine, measured 5.5 by 1.2 m and weighed around 18 tonnes, and as of 1999 a beryl from Malakialina in Madagascar, 18 m long and weighing 380,000 kg, was the largest known natural crystal of any mineral. Russia, Brazil and the United States lead production of common beryl for beryllium.
Its value spurred imitation. Carroll Chatham achieved the first commercially successful synthetic emerald, and Pierre Gilson's flux-grown stones, on sale since 1964, grow about 1 millimetre a month on colourless beryl seeds. Beauty comes with a hazard: beryllium compounds are carcinogenic, and inhaling dust can inflame the lungs, so miners and cutters must handle the material carefully.
Source: Beryl
