A lesson in hardness— A stone’s hardness is measured on a scale called the Moh’s scale. The scale measures from 1 (talc) to 10 (diamond). A small incomplete list follows that tables some of the common jewelry stones and their relative hardness.
Gems which are opaque do not show surface scratches as badly as faceted translucent stones, and therefore do not need to be as hard. Most opaque stones are polished into cabochons, with smooth rounded surfaces, as opposed to flat facets. Such gemstones include
All of the above are considered delicate materials and should be treated as such.