Why is the Blue Lagoon blue?

The Blue Lagoon Water contains a considerable amount of the chemical compound of silicon (represented by the symbol Si) and oxygen (represented by the symbol O). The compound contains twice as many units of O as Si and therefore has the chemical symbol SiO2. This is the white, clay-like substance that our visitors are so familiar with. The substance, commonly referred to as silica, reflects light in a way that gives the lagoon its characteristic blue color.

Sunlight contains all visible colors. Each color has its own wavelength. Red light has the longest wavelength, and blue the shortest, with other colors falling in between. When the Blue Lagoon Water cools, tiny silica particles (SiO2) precipitate. These particles are much smaller than the wavelengths of visible light, making it difficult for them to reflect light.

However, the silica particles do reflect relatively more of the shorter wavelengths, which are closer to their size. Since blue light has the shortest wavelength of the visible colors, it is the color that reflects the best when sunlight hits the silica in the water. As a result, the lagoon takes on its distinctive blue hue. This phenomenon is similar to why the sky appears blue.