Gemstone few as one in a million atoms. These so-called impurities are sufficient to absorb certain colors and leave the other colors unaffected. For example, beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If manganese is added instead of chromium, beryl becomes pink morganite. With iron, it becomes aquamarine. Some gemstone treatments make use of the fact that these impurities can be "manipulated", thus changing the color of the gem. Gemstones are often treated to enhance the color or clarity of the stone. Depending on the type and extent of treatment, they can affect the
Prong setting shapes, depending on the shape of the gemstone, the size of the gemstone, or whether or not the gemstone is faceted or cabochon shaped. Common shapes of heads used in stone setting include round, oval, emerald cut, princess cut, marquise cut, pear shaped and trillian cut. V-shaped prongs are recommended for a marquise-cut or pear-shaped stone, while flat prongs are recommended for a flat-cut emerald. A prong setting holds the gem securely while allowing the gem to be struck with more light and from more angles, increasing the brilliance of the gemstone. A prong setting offers less protection to the