The Mohs hardness scale
The Mohs hardness scale describes a scale from 1 to 10, which indicates the relative hardness of a mineral. Diamond is the hardest substance in the world and is therefore rated with the highest hardness grade of 10. To further illustrate the Moh's hardness it helps to imagine that a moonstone
(hardness 6) is about as hard as the blade of a kitchen knife. A fingernail would only measure a grade of 2-2.5 on the scale.
At Bron, the hardness plays a minor role. Our overriding selection criteria are color and the ‘liveliness’ of a gemstone.