Emerald is green gem beryl, Be3Al2Si6O18, in which the colouring agent is a minor amount of chromium or vanadium. Emerald is the third most valuable gemstone (after diamond and ruby) and can be worth more than $100,000 per carat. More than 30% of the world's emerald production is from Colombia; other producers are Brazil, Zambia, Zimbabwe, Madagascar, Afghanistan, Pakistan, and Russia. Much of the world production is from small-scale operations using technologically simple approaches. Modern mines have recently been constructed in Brazil using environmentally benign Dense Media Separation (DMS) mineral extraction plants, similar to those used in diamond mines. Consequently, small operations can be expected to produce a high profit / small volume commodity that can be easily transported from a remote location with minimal long-term environmental impacts.