NEW YORK (ETF Expert) -- Copper is one of the world's most popular metals. It is used in everything from water pipes to radiators to air conditioning systems. Some will say that the industrial metal possesses a Ph.D. in economics . . . it is that critical to world GDP growth.One country alone is responsible for about 40% of the world's copper reserves and roughly 35% of copper exporting. That country is Chile. In 2011, with emerging nations battling inflation and the European Union fending off member country bankruptcies, copper prices dropped into the septic tank. The perceived weakening of demand for industrial commodities weighed heavily on Chile's economic prospects and the share price of Chilean stocks.