With its startling blue-green hues, turquoise has been a treasured gem for thousands of years across many civilizations. Egyptian Pharaohs buried over 7,000 years ago have been discovered wearing turquoise bracelets, testifying to the early importance of the gem. Native Americans of the Southwestern United States traded with turquoise, as did Chinese and Persian cultures along the famous Silk Road. The birthstone for December, turquoise is a semi-precious gemstone that consists of the chemical elements copper, aluminum, phosphorus, hydrogen, and oxygen. Deposits usually occur in areas with some volcanic or thermal history. Other minerals entering into the stone's structure create color variations, but most turquoise is concentrated near the copper-aluminum end of this spectrum, making it typically closer to blue or blue-green than to green or green-blue.