The Mohs Scale of Hardness is a relative scale of hardness based on ten minerals that are readily available that range from very soft to very hard. Diamond is the hardest known naturally occurring substance and this is what Austrian mineralologist Friedrich Mohs put at the top of the scale, developed in 1812. Substances are then measured against the scale by finding out the hardest material it can scratch and the softest material it can be scratched by.
Knowing where gemstones lie on this scale helps jewellers decide which to choose for a particular design. For example, Amber lies at 2.5 on the scale and so will need a setting that protects it. Rings take a bit more “punishment” compared to a necklace or earrings and so any gemstones set in rings need to withstand daily wear.