Cleopatra prized her emeralds more than any other gem. The Romans also loved emeralds because, as ancient scholar Pliny said, “nothing greens greener.” The extreme rarity of transparent emerald is why the finest quality emeralds can be more valuable than diamonds. Emerald’s rich green color is caused by minute traces of chromium or vanadium. The more vivid the green, the more valuable the emerald. Sometimes emeralds are even carved. Why would anyone choose an emerald engagement ring? Interestingly the emerald was Cleopatra’s favorite gemstone.