The price of gold has hit all-time highs recently, touching $1,800 an ounce as the stock market swooned last Wednesday. But there's another commodity that's enjoying an even bigger bull market these days: rhino horns. According to a recent study by Kenya-based ivory expert Esmond Martin, and his colleague Lucy Vigne, the ivory trade is hotter than ever, fueled by booming demand in China, where it is coveted for its supposed medicinal purposes. The study found that the number of ivory items on sale in southern China has more than doubled since 2004. And most of it is traded illegally.