Tenacity (Toughness)

Tenacity, or toughness, is the cohesiveness of a mineral. It is the resistance the mineral or gemstone offers to breakage. Tenacity and hardness, though not necessarily related, are factors that determine the durability of a gemstone.

Despite their incredible hardness (10), diamonds are relatively brittle because of their excellent cleavage. Nephrite Jade has a Mohs hardness of only 6-6.5, but is not easily broken.

Tenacity is given in degrees of toughness:

  • Exceptional, as in Jadeite and Nephrite
  • Excellent, as in Sapphire
  • Good, as in Quartz and Spinel
  • Fair, as in Tourmaline
  • Poor, as in Feldspar and Topaz