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Ammolite gems are special fossils that shine with rainbow colors. Most ancient fossils stay in dull shades of brown or gray. These unique gems are often used to make beautiful jewelry. For a long time, scientists could not explain how they got such bright colors. Now, researchers have finally found the answer. This discovery reveals a hidden secret inside ancient stones.
Ammolite comes from the fossilized shells of creatures called ammonites. These animals looked like modern squids and lived when dinosaurs roamed the Earth. The secret to their colors lies in the layers of their shells. This material is known as nacre or mother-of-pearl. However, not all shells with nacre shine like rainbows. Other shells, such as nautilus or abalone, do not show these brilliant colors either.
Scientists wanted to understand what made ammolite so colorful. They studied the tiny crystal plates inside the nacre under powerful microscopes. They examined ammolite, other fossils, and shells from nautilus and abalone. Two things stood out in the colorful stones. First, the crystal layers had a very uniform thickness. Second, thin gaps of air separated the plates. Only when the nacre had both features did the rainbow colors appear.
The researchers shared their discovery on October 30 in the journal Scientific Reports.
Hiroaki Imai is a materials scientist who first saw ammolite at a mineral fair in Tokyo. He was astonished to learn that the fossil itself was the source of the colors. Imai works at Keio University in Japan. He led a team that studied ammolite under powerful electron microscopes.
The gems they studied came from Alberta, Canada. These fossils are about 75 million years old. The team found a clear link between the crystals and the color. Ammolite with thinner crystal plates reflected blue light. Pieces with thicker plates reflected red light. This shows how size changes the color we see.
They also saw how ammolite differed from duller shells. In ammolite, thin pockets of air separated the crystal plates. These gaps were about 4 nanometers wide. That is about twice as wide as a single DNA molecule. In the fossil, old organic material wore away over time. This process left these perfect gaps between the crystals.
He’s part of a team that looked at pieces of ammolite under electron microscopes. The gems came from the Bearpaw Formation in Alberta, Canada. Fossils there date back about 75 million years.
In abalone shells, a thicker layer of material sat between the plates. In a dull ammonite fossil from Madagascar, the plates had collapsed completely. There were no gaps left at all. This proves that empty space is needed for the shine.
Computer models showed why the 4-nanometer gap was perfect. Plates packed too tightly did not reflect much light. This made the colors look dull and dark. Plates spaced too far apart reflected too many colors. These colors mixed together, which muddled the light. The team also saw that in a single piece, the layers were mostly the same thickness. This helped the stone reflect one distinct, bright color.
Imai says there may be two reasons only some fossils become colorful ammolite. It might depend on the type of ammonite that formed the shell. It also might depend on exactly how the fossil formed underground. These conditions are very special and hard to find.
For their next project, his team is looking at a different gem: opals. Opals are made of silica and form from weathered rock. Some types of opal exhibit vivid structural colors. Imai says his team wants to see if similar rules create the colors in those beautiful stones. They hope to find similar patterns of light and air.
The discovery helps us understand the hidden science behind ancient beauty. It shows how tiny gaps of air can create massive color. This knowledge might help scientists find new ways to make colorful materials. Engineers could use these ideas to build better displays or paints.
The story of ammolite shows how nature can create magic. Tiny structures inside a stone can control light in amazing ways. Scientists are now looking deeper into these secrets. They want to know how to copy this natural magic in our modern world. The process of nature turning simple shells into glowing gems is still not fully understood. But the new findings give us a big clue. The size of the crystals and the width of the air gaps are the keys. If these parts change even a little, the light changes too. This explains why some ammonite fossils are dark while others sparkle. It also explains why the colors shift as you move the stone. The light bounces off the layers in a specific pattern. This pattern depends on the exact angle and the spacing of the plates. Without the air gaps, the light would pass through or be absorbed. The gaps act like tiny mirrors that bounce the light back. This creates the strong and vivid colors we see. The study proves that the structure of the fossil is more important than the material itself. Even an old, dead shell can become a rainbow if the layers are just right. This is a surprising result from studying rocks that have been buried for millions of years. The findings open new doors for science and technology. People might learn how to make new materials that look like ammolite. These materials could be used in solar panels or protective coatings. Nature has solved complex problems of light control long before humans existed. We are only just beginning to understand how these ancient solutions work. The next time you see a shiny ammolite gem, remember the tiny air gaps inside. They are the reason the stone glows with so much color. The secret of the rainbow is found in the small spaces between the crystals.