Named for German mineralogist Friedrich Mohs (1773-1839), the Mohs scale is widely used as a hardness standard for gems and minerals. The concept is simple, employing what is often called the “scratch test.” Once Mohs determined that diamonds were the hardest of all materials, he assigned it his highest possible number, Mohs 10 (Diamond). He then sought the softest mineral he could measure, talc, and gave it the number 1. To establish a relative rating for all the common gems and minerals, Mohs rubbed hundreds of materials together. The one that scratched the other received a higher number on his scale. Knowing this concept prepares you to keep your harder gemstones from scratching softer gems and jewellery metals.