Turquoise Screwback Earrings Beautifully figured turquoise screw-back earrings. Subtle, but strong in colour - just enough to cause impact. The earrings are 1/2" in diameter. Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. These are all small-scale, often seasonal operations, owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization.