The term tenacity refers to a mineral’s toughness and its resistance to breaking or deformation. Those that break, bend, or deform easily have little tenacity. In contrast, strong unbreakable minerals have great tenacity. The photo here shows samples of the gemstone jade shaped and polished to produce a figurine and a cabochon. Gemmy jade may be either of two kinds: jadeite (a pyroxene) or nephrite (a rock containing very fine-grained green amphibole). In either case, jade is one of the most tenacious natural materials known. It does not easily break or deform, even when under extreme stress. That is one reason, besides beauty, that it is prized as a gemstone.
The nature of its chemical bonds controls a mineral’s tenacity. Ionic bonding often leads to rigid, brittle minerals. Halite is an excellent example of a brittle mineral. It shatters into many small pieces when struck. Quartz, too, is brittle, although the bonding in quartz is only about half ionic. Many metallic minerals, such as native copper, are malleable, which means we can shape them with a hammer. Native copper is also ductile, which means we can stretch it out into wire-like shapes. Other minerals, such as gypsum, are sectile, which means they can be cut into thin pieces with a knife.
Some minerals, including talc and chlorite, are flexible due to weak van der Waals and hydrogen bonds holding well-bonded layers of atoms together. When force is applied, slippage between layers allows bending. When pressure is released, they do not return to their original shape. Still other minerals, notably the micas, are elastic. They may be bent but resume their original shape after pressure is released if they were not too badly deformed. In micas and other elastic minerals, the bonds holding layers together are stronger than those in chlorite, clays, and other minerals with layered atomic arrangements.
Thus, we have a number of terms that we can use to describe mineral tenacity:
|Terms Used to Describe Tenacity|
|brittle||easily broken or powdered|
|malleable||capable of being hammered into different shapes|
|sectile||capable of being cut into shavings with a knife|
|ductile||capable of being drawn into a wire-like shape|
|flexible||capable of being bent into a different shape|
|elastic||a bendable mineral that returns to its original shape after release|