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
Varieties of Arabic sedentary varieties and the rural varieties within the Arabian peninsula are even more conservative than those elsewhere. Within the sedentary varieties, the western varieties (particularly, Moroccan Arabic) are less conservative than the eastern varieties. A number of cities in the Arabic world speak a "Bedouin" variety, which acquires prestige in that context. When it comes to phonetics the Arabic dialects differ in the pronunciation of the short vowels (, and ) and a number of selected consonants, mainly , and the interdental consonants , and , in addition to the dental . Emphasis spreading is a phenomenon where is backed