Celebrate the Holiday Season with the Museum’s Stunning Collection of Blue Specimens

Learn how this rare hue shows up in the natural world with some of the Smithsonian’s bluest specimens

A blue bird with white and grey spots lies against a white background.
Celebrate the Holiday Season with the Museum’s Stunning Collection of Blue Specimens. Smithsonian Institution

This time of year, the color blue is everywhere from holiday lights and decorations to blue-tinted snow and icicles. But blue is actually one of the rarest colors in the natural world, where shades of browns and greens dominate nature’s palette.

Because of its rarity, any natural burst of blue is often eye-catching. To show off one of nature’s most brilliant phenomena, the National Museum of Natural History’s Objects of Wonder exhibition features several of the museum’s bluest specimens from reflective butterfly wings to ultramarine minerals. 

In celebration of the approaching winter holidays, Smithsonian Voices took a closer look at these radiant specimens to reveal the science behind nature’s bluest blues.

Why is Blue so Rare?

The greens and browns that color the natural world come from chemical compounds called pigments.These pigments absorb and reflect specific wavelengths (and thus colors) of light. 

For example, plants have chlorophyll pigments in their stems and leaves that absorb sunlight for the plant’s cells to turn into energy. Chlorophyll can absorb light in the red and blue spectrum, but it cannot absorb green light. That’s why we see plants as green – the light that isn’t absorbed is reflected back to our eyes. 

But in nature, true blue pigments – or pigments that reflect pure blue light – are very hard to come by. Less than 10% of the world’s plant species have blue pigmented flowers, and there are only a handful of animal species that produce a true-blue pigment. But the rarity of true-blue pigments has not stopped some animals from displaying blue colors without them. And taking a close look at the atomic elements and structures present in minerals can account for their blue hues.

Synchiropus splendidus

The vibrant stripes on this mandarinfish specimen may serve as a warning to keep predators at bay. Smithsonian Institution

The mandarinfish (Synchiropus splendidus), is one of only two vertebrate species on earth that produce a true-blue pigment. The small, brilliantly colored tropical fish is native to the Western Pacific and this specimen was collected from the Palau Islands, an archipelago north of Indonesia. While mandarinfish look beautiful, you wouldn’t want to approach one in the wild. Because mandarinfish lack scales they are coated in a thick protective layer of toxic, foul-smelling mucus. 

Mandarinfish owe their striking blue markings to at least two types of pigments in their cells: true-blue cyanophores and blue-red cyano-erythrophores. Scientists posit that these  bright colors may serve as a beaming warning for predators to stay away from its toxic mucus coating.

Blue Morpho Butterfly

The blue morpho butterfly may appear blue, but its true pigment is actually brown. The microscopic structure of its wing scales creates this optical illusion. Smithsonian Institution

The blue morpho butterfly (Morpho menelaus) is another striking example of blue in the animal kingdom. This specimen was collected from the museum’s O. Orkin Insect Zoo, but the species’ native range spans Central and South America from Costa Rica to southern Brazil. Blue morphos are one of the largest butterfly species in the world – their iridescent blue wings can grow to be 8 inches across.

Unlike the mandarinfish, the blue morpho does not produce true-blue pigments. A clue to how it creates this color lies in its iridescence. If you look at a blue morpho’s wings from different angles, the color changes. This indicates that the color is not produced by pigments, but by microscopic light-bending structures on the surface of its wings. While it may look like the blue morpho’s wings are truly blue, their pigmented color is actually brown. “Nature is endlessly wondrous and deceptive,” said Smithsonian research entomologist Robert Robbins, the museum’s curator of butterflies. 

Structural colors are created by the physical form of an organism or object. Observing a blue morpho wing under a microscope reveals thousands of tiny grooved scales. When light hits them, the arrangement of the grooves manipulates light so that only blue wavelengths are reflected back to the eye. 

Why have blue morphos evolved to exhibit color through structures rather than pigments? According to Robbins, the short answer is that we don’t know. But there are some theories. A butterfly’s colorful wings aren’t just used for flight, they’re also used for communication. Like the mandarinfish, their bright colors may signal to a predator that they are poisonous. It also may help them woo a prospective mate. 

White Opal

The multi-colored flecks that give this white opal its iridescent shimmer are a result of microscopic silica spheres. Smithsonian Institution

This triangular cabochon-cut white opal came to the Natural History Museum from the famous opal fields of Andamooka in South Australia. Like the blue morpho butterfly, this vivid gemstone showcases its color through structure. 

While the dominant color in the opal is white, flecks of blue, pink, red and green give it a rainbow-like sparkle. That iridescence — which gem scientists refer  to as “play of color” — is created by the microscopic spheres that make up an opal’s structure. Those spheres are made of silica and packed tightly together with more silica and water filling in the gaps between them. 

The spheres act like diffraction gratings: when light hits them, it splits into its component wavelengths. But the colors we see depend on the size of the spheres. Blue iridescence is created by smaller spheres that scatter blue and violet light waves. But according to Gabriela Farfan, the museum’s curator of gems and minerals, “It’s still a bit of a mystery as to exactly how these colors come about.”  She stresses that more research is needed to fully understand the complex, light-splitting structure of opals. 

Blue Flame – Lapis Lazuli

This massive lapis lazuli specimen is one of the NMNH’s largest gemstones. Smithsonian Institution

It’s easy to see where this stunning, 250-pound slab of lapis lazuli gets its name. Swirls of white calcite stand out against its brilliant blue hue, giving the rock a flame-like appearance. This specimen hails from the Hindu Kush mountains in the northeast corner of Afghanistan, where the majority of the world’s supply of lapis lazuli is mined. Miners then use mules to transport many of these gems – including the Blue Flame – over treacherous mountain terrain.

Unlike opal, lapis lazuli does not get its color from its structure. It’s technically a rock, which means that it’s composed of multiple different minerals that have aggregated into a single solid. Lazurite is the most abundant mineral in lapis lazuli, followed by varying amounts of calcite (which appears as white swirls) and pyrite, which can create sparkling flecks of “fool’s gold”. But lazurite – and more specifically, its sulfur content – is what makes this gemstone blue. Sulfur in the lazurite crystal structure absorbs all wavelengths of light except for blue light. 

Lapis lazuli has been an important source of blue pigment in many cultures. Until the 1800s, the deep shade of blue that painters call “ultramarine” was made by crushing lapis lazuli and mixing it with binding agents. This made ultramarine incredibly expensive – which did not stop the Renaissance painters that coveted the shade. Today, ultramarine is artificially manufactured to meet artists' demands. 

Aquamarine Beryl

Beryl (var. aquamarine) from Diane’s Pocket in Colorado. Smithsonian Institution

Usually, gem-quality aquamarine crystals (the blue variety of mineral beryl) like this come from Brazil. But this specimen didn’t travel nearly as far to get to the museum. It was extracted from Diane’s Pocket, which is a rock cavity lined with crystals in Colorado. These cavities, known as vugs or “pockets,” contain crystals like beryls, which have an elongated, hexagonal shape. Aquamarine is the gem name given to blue beryls.

Aquamarine gets it’s pale-blue color from tiny trace amounts of iron within the mineral. Farfan likens them to food coloring:if you add a drop of blue food coloring to a vanilla cake, it will turn the whole cake blue, but it won’t change the flavor. Trace elements change the color of a mineral, but they don’t change its chemical composition. Like the sulfur in lazurite, iron absorbs all colors but blue light, and thus its presence lends a sky-blue tint to aquamarine beryls.

Roman Glass Vessel

Years of weathering have allowed the atomic elements in this glass vessel to show their true colors. Smithsonian Institution

The ancient art of Glassmaking dates back 4,000 years. In ancient Rome, glassmakers manufactured vessels like this one for storing and serving food and drinks. This specimen was forged between 100 BCE and 200 CE and found in Cyprus or Egypt. 

Glassmakers back then – and to this day – use minerals to give their glassware different tints. Like the aquamarine beryl, iron in the sand used to make this vessel gives its patina a light blue tint.

Its iridescence, however, is another example of structural color. This vessel was buried with its owner as a funerary offering. Over time, natural weathering turned the glass opaque and produced its shimmering finish. 

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