Hardness
Hardness is the resistance a mineral offers when we try to scratch its surface with a hard object. In 1812, German mineralogist Friedrich Mohs created a hardness scale by selecting 10 minerals as standards for relative hardness, where each mineral on the scale can scratch a mineral with a lower hardness. The hardness of a mineral is determined by the nature of the chemical bonds in its crystal structure. Diamond and quartz are very hard because they have three-dimensional lattice structures with covalently bonded atoms. Native metals like aluminium and gold are soft because they have tightly packed atoms with metallic bonds.
Kyanite – The hardness of the mineral varies depending on the direction of scratching. A good example of anisotropy in hardness is the mineral kyanite. Parallel to the crystallographic axis c, it has a hardness of 5½, but parallel to the crystallographic axis a, it has a hardness of 7. Therefore, a steel needle will easily scratch the kyanite crystal parallel to its longer axis (axis c), but perpendicular to it (along axis a), the steel needle will not be able to scratch it. The outdated name for it is disten, from the Greek words δίς (dis) – two and στενός (stenos) – strong, hard, referring to its unequal hardness in different directions. This anisotropy in kyanite can be considered an identification characteristic.
Mohs’ scale of hardness shows the relative hardness of minerals. When we compare Mohs' hardness scale to absolute hardness, we see that Mohs' scale is not linear. The hardness of the softest minerals is closer to each other than the hardness of the four hardest (quartz, topaz, corundum, diamond). Gypsum, with a hardness of 2, is only slightly harder than talc with a hardness of 1, but diamond (10) is five times harder than corundum (9).
Ljudevit Vukotinović
Ljudevit Vukotinović (1815 – 1893), a nobleman from the Farkaš family, also worked on creating Croatian mineralogical and petrographic terminology.
Learn more