How hard are emeralds compared with other gemstones?
The hardness of a material is the resistance the material has to scratching. The Moh’s scale of hardness places emerald hardness between 7.5-8.5, meaning it will be scratched by minerals with hardness equal or superior to it. The hardness of emerald is below that of diamond (10) and corundum (9). However, emerald, because of its irregular cleavage, is difficult to simply fracture. The toughness, which is the resistance to breakage, is considered medium-high in emeralds, as it is in other gemstones.
