



Crystal Structure is the fundamental building block of a mineral. It describes the simplest alignment of atoms needed to define the structure of a mineral. There are seven systems or structures that are further characterized by their axis length, the angles between their axis, and finally the number of symmetry centers contained within the group. A mineral's atomic structure actually is responsible for many of its physical properties. An understanding of the crystal structure and the particular elements used in the creation of a mineral provides a good deal of insight to its physical properties. Density (specific gravity), hardness, cleavage, fracture, toughness, and color are all strongly related to the structure and elements contained within a mineral. Density, the measure of a minerals mass to volume, is related to the specific element's that make up the mineral, and their individual atomic weights. High atomic weight elements mean higher density. A compact crystal structure will aid in driving the density up as a tighter packing pattern means more atoms per unit cell. Hence minerals containing lead, barium, or any elements in the 5th row of the periodic table will show much higher density due to their atomic numbers. Minerals comprised mainly of Si, O, Al, Na, K, Mg or other 2nd and 3rd row elements will tend to have average density values. Density is thus a function of elemental make-up and the crystal structure of the mineral.