Emeralds are medium to dark green beryl which derives its color from chromium and vanadium. Emerald of fine color and clarity can be quite expensive. Almost all emeralds contain numerous small inclusions and fractures that promote fragility. Most stones on the market are impregnated with oils, waxes, or other substances to mask the fractures and sometimes enhance color. Emeralds in antiquity were mined by the Egyptians, in Austria and northern Pakistan. A rare type of emerald known as a trapiche emerald is occasionally found in the mines of Colombia. The best known sources include Colombia and Zambia. Fine emeralds are also found in other countries such as Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia. In north America emeralds can be found in North Carolina and were also discovered in the Yukon.