Emerald belongs to the important group of beryl gemstones. There are quite a few different gemstone-quality varieties of beryl, most of which are classified based on color and coloring agents, such as pink morganite and red bixbite. There are also many other green colored gemstones that can be confused with green emerald, including aventurine, demantoid garnet, tsavorite, chrome tourmaline, chrome diopside, grossularite, uvarovite, verdelite, fluorite, hiddenite and peridot. Oiling is a common emerald treatment and in most cases, it is done right at the mining location. The term 'oiling' refers to the practice of immersing emeralds in a colorless oil or resin (most often cedar oil) in order to enhance color, clarity and stability.Emerald is the most precious stone in the beryl group. The name comes from the old French word 'esmeralde', which was derived from the Greek word 'smaragdos' meaning 'green stone'. By definition, emerald is any medium to dark green beryl colored by chromium. Green beryl colored only by vanadium is not considered to be true emerald, but rather as simply green beryl.