Topaz obtains much of its popularity from its beautiful colors and its status as a birthstone. Natural topaz colors include rare and valuable yellow, orange, pink, red, purple, and blue. One of the best-known physical properties of topaz is its hardness. It has a hardness of 8 on the Mohs hardness scale, making it the hardest silicate mineral. It also serves as the Mohs hardness scale index mineral for a hardness of 8.