The natural samples of corundum pictured below show variations of color from red (ruby)to blue (sapphire).The differences in color is best explained by:

Question

Quizplus · Accepted Answer

The principle of atomic substitution refers to the fact that minor impurities of other elements can replace atoms in the crystal lattice of corundum, leading to variations in color. For example, chromium impurities can cause the red color in ruby, while titanium and iron impurities can lead to the blue color in sapphire. Polymerization and polymorphism refer to different aspects of the crystal structure, but do not explain the color variations seen in corundum.

The Natural Samples of Corundum Pictured Below Show Variations of Color