A gemstone's ability to avoid scratching is determined by it's hardness level from 1-10 the Mohs scale. The hardest gemstone on the scale is diamond, which means it cannot be scratched by any other material beneath it on the scale. This makes diamonds perfect for engagement rings and other pieces of jewelry you would wear on a daily basis. Gemstones that rank 7.5 to 8 on the Mohs scale are generally quite durable, but should still be handled with care. A number of popular gemstones such as opal, moonstone and turquoise rank from 5-6 on the Mohs scale and are considered more fragile.