Earth

Opals and emeralds

Opal is one of the most fascinating gems in the world thanks to its changing colours. The mineral is made of hydrated silica (SiO2.nH2O, this means that the mineral structure also includes water molecules) and it is shapeless. The most appreciated varieties are: noble opal, milky and with vivacious iridescence, harlequin opal, and fire opal, which is more transparent than noble opal and has a bright orange colour. The turquoise variety has a cerulean colour and looks like porcelain. The most beautiful examples come from Iran, while the American turquoise variety is less valuable since it is more degradable. The name emerald comes from the Greek "smaragdos", which means green stone. The most ancient deposits, exploited by Pharaohes, were located on the Egyptian coast of the Red Sea. At the moment, most of the production comes from Columbia, Brazil and the Ural Mountains. The green colour of emeralds is due to the presence of vanadium and chromium oxide.