Carl Friedrich Christian Mohs was a German chemist and mineralogist. He was the creator of the Mohs scale of mineral hardness. Mohs also introduced a classification of the crystal forms in crystal systems independently of Christian Samuel Weiss.
Friedrich Mohs, 1832
Memorial plaque in Vienna
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical properties of minerals and mineralized artifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.
Page from Treatise on mineralogy by Friedrich Mohs (1825)
Calcite is a carbonate mineral (CaCO3) with a rhombohedral crystal structure.
Aragonite is an orthorhombic polymorph of calcite.
The perovskite crystal structure. The most abundant mineral in the Earth, bridgmanite, has this structure. Its chemical formula is (Mg,Fe)SiO3; the red spheres are oxygen, the blue spheres silicon and the green spheres magnesium or iron.