Final answer:
The blue color of topaz is typically achieved through irradiation and heat treatment, which alter the gemstone's crystal structure and result in a change in how it absorbs and reflects light. This process is similar to how other colored gemstones obtain their hues from trace elements like iron, titanium, or chromium.
Step-by-step explanation:
The popular blue color of topaz can be achieved by treating colorless or lightly colored stones with intense heat and radiation methods. This process is known as irradiation, which followed by heat treatment can cause the stone's color to change to the desired deep blue. In the case of topaz, as well as for other gemstones, the color alteration results from defects and impurities within the crystal structure caused by the treatment, which affects the way the stone absorbs light and, consequently, its appearance. A similar principle is observed in the creation of colors of other gemstones, like the presence of trace amounts of elements such as iron and titanium giving blue sapphire its characteristic color or chromium impurities imparting a red or green hue to rubies and emeralds, respectively.