WHAT DOES HARDNESS MEAN IN REFERENCE TO GEMSTONES AND DIAMONDS?

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 which is harder between a feather and glass, they’ll say feathers are soft and glass is hard. In the world of gemology, however, glass is soft. It can be scratched easily by a variety of what gemologists consider hard substances.

Hardness depends on the bonds that hold the atoms together within a crystal structure. This bonding is reflected in the ease with which the layers of atoms at a surface can be separated by applying pressure with a sample of another material. If the second material is harder than the first, it’ll leave a furrow, or scratch. That represents the breaking of millions of atomic bonds on a microscopic scale. The hardness of a mineral is, specifically, its “scratchability”. Every mineral can be ranked based on those others minerals it can scratch.

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 one 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 RZ® Simulant Diamond (9.5) is almost twice as hard as topaz (8), and diamond (10) is four times as hard as the RZ® Simulant Diamond.

A diamond is both hard, defined scientifically, and brittle. The steel of a hammer (hardness 5 or 6) won’t scratch a diamond, but it can shatter a diamond. Assuming you don’t regularly take a hammer to your jewelry, scratching is a hazard encountered more frequently. Think of how many times daily you put your hands inside pockets, purses, glove compartments, and desk drawers. Now think of what brushes against a ring when you do those things. The scratches that could develop from this may be tiny, even microscopic, but they can accumulate and be visible over time.

Gemstone hardness alone isn’t a measure of a stone’s wearability or toughness. Several factors have to be considered together to determine how well a gem will wear. Please visit our FAQ on how to take care of your RZ® Simulant Diamond for cleaning and wear instructions.