Hardness with reference to gemstones is often misunderstood. The word “hardness” has a very specific scientific meaning in gemology that differs considerably from its everyday usage.The scientific definition of hardness is the ability to resist scratching, nothing more. For example, if you asked someone if a feather and glass are soft or hard, they’ll say feathers are softand glass is hard. In the world of gemology, however, glass is soft. It can be scratched easily by a variety of what gemologists consider harder substances.The Mohs scale was created to be a reference for the 10 most common minerals ranked in order of increasing hardness. At the top of the scale is diamond (10) and directly below it is Corundum (9), which is what rubies & sapphires are made from.Each of these minerals can be scratched by the substances above it and will scratch the ones below it. Minerals of the same hardness won’t scratch each other. Thus, a ruby can’t scratch a sapphire and vice versa.A diamond is much harder than corundum, even though they’re only one division apart on the scale. The Mohs scale starts approximately linear, but the curve climbs sharply at the high end.The Diamond Hybrid (8.8) is almost twice as hard as topaz (8), and diamond (10) is four times as hard as the Diamond Hybrid.