There are a number of objects in nature that exhibit a blue color without the need for artificial dyes or pigments. The blue color comes from structural properties that reflect blue wavelengths of light. Some common examples of naturally blue objects are the sky, certain minerals, some plant structures, and the feathers or scales of certain birds, insects, and fish. In this article, we will explore some of the more common naturally occurring blue objects.
The Sky
One of the most ubiquitous naturally occurring blue objects is the daytime sky. On a clear day, the sky appears as a light blue color. This is due to a phenomenon called Rayleigh scattering. As sunlight passes through the atmosphere, the shorter wavelengths of blue light are scattered more than longer wavelengths. The scattered blue light is what gives the sky its characteristic color. The exact shade of blue depends on the amount of moisture and dust particles in the atmosphere. After sunset, the sky can also often appear blue due to the scattering of city lights.
Water
Clear, deep bodies of water can also appear blue, again due to the physical scattering of light. As sunlight enters water, the red end of the visible light spectrum is absorbed more readily than blue. The water molecules then scatter the remaining blue wavelengths, causing deep oceans, lakes, and rivers to take on a blue hue. However, water close to shore generally appears more green or gray because of the reflection of sand or sediment from the bottom.
Blue Minerals
There are a number of naturally occurring minerals that contain blue pigments. Some examples include:
| Mineral | Chemical Composition |
| Azurite | Copper carbonate hydroxide |
| Lazurite | Sodium, calcium, and aluminum silicates containing sulfur |
| Vivianite | Hydrated iron phosphate |
| Blue calcite | Calcium carbonate with mineral impurities |
These minerals get their blue color from their unique chemical makeups that allow them to absorb other wavelengths while reflecting blue. These minerals are used as gemstones and pigments and are mined in locations around the world.
Blue Flowers
There are a number of flowers found in nature that exhibit blue coloring without artificial dyes. Some examples include:
| Flower | Genus |
| Bluebell | Hyacinthoides |
| Forget-me-not | Myosotis |
| Cornflower | Centaurea cyanus |
| California lilac | Ceanothus |
| Morning glory | Ipomoea |
The blue pigments in these flowers come from anthocyanins, flavonoid compounds that reflect blue and ultraviolet light. The concentrations and combinations of anthocyanins produce different shades of blue. Other plant structures, like blueberries, also contain natural blue pigments from anthocyanins.
Blue Feathers
Many species of birds naturally grow brilliant blue feathers without the need for pigments or dyes. The most well-known example is the Blue Jay, which gets its name from its vivid blue wing and tail feathers. The blue color is created by the physical structure of the feathers, which have layers that reflect blue light. Other birds with structurally blue feathers include bluebirds, indigo buntings, and some species of parrots and macaws. The highly metallic feathers of peacocks are also structurally blue.
Blue Insects
In addition to birds, some species of insects also exhibit blue coloration for structural reasons. A common example is the Morpho butterfly. The bright blue wings of the Morpho butterfly contain microscopic scales that reflect blue light waves. Other blue insects include certain dragonflies, damselflies, and weevils. In some cases, the blue may come from pigments as well as structural coloration.
Blue Fish
The scales or skin of some fish species can appear blue due to the physical scattering and reflection of light waves. For example, the scales of blue tang fish contain a crystalline material called iridophores. These reflect blue light and create the vibrant color. Other naturally blue fish include blue catfish, blue sharks, blue hippo tangs, and parrotfish. The meat of these fish does not retain the blue color when cooked, as it comes from the reflective properties of the skin and scales.
Blue Gems
In addition to blue minerals like azurite and lazurite, some gemstone varieties naturally exhibit blue coloration. These include:
| Sapphire | Aluminum oxide |
| Blue zircon | Zirconium silicate |
| Tanzanite | Calcium, aluminium hydroxyl silicate |
| Blue topaz | Aluminum fluorosilicate |
Trace impurities in the crystalline structures of these gems allow them to selectively reflect blue wavelengths, producing brilliant blue hues. These can occur naturally or be enhanced through artificial treatment. Blue gems have been treasured throughout history for their rarity and beauty.
Blue Foods
There are also some naturally blue foods that get their color from plant pigments. For example:
| Blueberries | Anthocyanin pigments |
| Blue potatoes | Anthocyanin pigments |
| Blue corn | Anthocyanin pigments |
| Blue cheese | Penicillium mold spores |
When cooked, the proteins and acids in some blue foods can cause the color to turn more green or gray. But natural blue plant pigments are responsible for giving foods like blueberries their quintessential color.
Blue Animals
Beyond birds, insects, and fish, some other animals naturally exhibit blue coloration. This includes:
| Blue poison dart frog |
| Blue glaucus sea slug |
| Blue dragon sea slug |
| Eastern blue-tongued lizard |
| Blue sheep (Bharal) |
In amphibians, reptiles, and some mammals, blue skin and hair color comes from specialized pigment cells. The specific blues can range from light powder blue to deep navy. These colorful creatures use their blue hues as camouflage or to warn potential predators that they may be poisonous.
Conclusion
While many manmade objects are dyed or painted to achieve blue color, there are also a plethora of naturally occurring blues found in nature. From the sky overhead to gemstones underground, blue wavelengths of light are reflected and scattered to produce brilliant naturally blue objects. The variety of mechanisms, from molecular pigments to the physical structure of proteins, minerals, and plants, demonstrate the many ways that vivid blues form in the natural world. So the next time you admire something blue, it may not be from artificial coloring, but a product of physics, chemistry, and evolution.
