In the book "Firefly Guide to Gems," Cally Oldershaw observes that colored gemstones achieve their varied hues according to the type of light they absorb or reflect. Reflected light is not the only factor that determes color, however; the presence of trace amounts of minerals such as iron, titanium, chromium, vanadium, copper and manganese also influence a gem's tint. Gemstones may be pale or bright in color, and every tone in the rainbow has its corresponding gem.
Red
Red gemstones are available in a wide range of shades, from the subtle pinkish red of a tourmaline to the orange-red of carnelian to the deep red of a garnet. Perhaps the most famous, and most prized, red gemstone is the ruby. According to Mindat.org, a ruby must be deep red and flawless to possess any value.
Blue
Ask someone to name a bright blue gemstone and he will undoubtedly reply, "sapphire." These intensely blue gems --- a variety of corundum --- are some of the most coveted stones in the world. Other bright blue stones include lapis lazuli, iolite, and indicolite tourmaline, but many would agree that none of these match the beauty of the sapphire.
Green
Bright green gemstones include emeralds, peridot, dioptase, tourmaline and chrysoprase. Of these, the most highly valued is the emerald, a variety of beryl. Most emeralds come from Colombia. It is rare to find an emerald that is free from inclusions; therefore, those that are without flaw are highly coveted.
Violet
Amethysts come to mind immediately when thinking about violet gemstones, but other bright violet stones can be found in diamonds, sapphires and spinels. Kunzite is another violet gem.
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