While studying hackmanite, a mineral that typically forms in alkaline, low-silica magma, researchers found that it can change color when exposed to repeated UV rays without being damaged.

A research group at the University of Turku in Finland has been studying the properties of the strange material, and developing it for nearly a decade, and have been able to launch applications such as personal UV monitoring and X-ray imaging, based on the ability of hackmanite to change the color.

The study, published in The Proceedings of the National Academy of Sciences PNAS, on June 2, showed that hackmanite is a material that is characterized by its high durability, formability, application and employment for various purposes. .

A wonderful natural substance

Geologists first described the mineral in the 19th century, and were fascinated by its tendency to glow softly when broken or placed in the dark, and then lose its glow back in the light.

Hackmanite is known for its ability to show reversible photochromism when exposed to ultraviolet and X-rays, and natural hackmanite has found a distinct use, in gemstones because of this property.

An international multidisciplinary team had revealed how certain types of hackmanite retain their glow during their transition from light to dark, and their previous study, published in the journal Chemistry of Materials, showed that the key to this property is the precise interaction between the natural impurities of the mineral, and determined by how it is configured.

The structural features enable the hackmanite to change color from white to purple under UV irradiation and eventually return to white in the absence of radiation.

Recently, when studying 3 natural color-changing minerals, Hackmanite, Tugtupite, and Scapolite, the researchers found that the natural minerals examined are inorganic natural materials, but have organic impurities, such as hydrocarbons, that can change color. Reversely due to exposure to radiation.

However, these hydrocarbons can only change color a few times before their molecular structure breaks down, because changing the color involves a drastic change in the structure, and undergoing this change repeatedly eventually breaks the molecule.

“In this research, we discovered for the first time that there is indeed a structural change involved in the color-changing process as well. When the color changes, the sodium atoms in the structure move relatively far from their usual places and back again,” says Mika Lastosari, professor in the Department of Chemistry at Finland's University of Turku. This can be called structural breathing, and it does not destroy the structure even if it is repeated a large number of times."

The researchers demonstrated that hackmanite's ability to alternate between white and violet hues is highly repeatable, and according to Altossari, the durability is due to the strong, three-dimensional cage-like overall structure of these minerals, which is similar to that found in zeolite.

White scapolite turns blue under ultraviolet rays (University of Turku)

Sodium atoms

As reported in the study’s press release published on the “eurekalert” website on June 21, as Sami Faurie, a doctoral student at the University of Turku explains, “In these color-changing minerals, the cage-like structure allows for atomic movement inside while maintaining The cage itself is intact. This is why metals can change color and return to their original color practically indefinitely."

Previously, scapolite was known to change color much faster than hackmanite, while togtopite changes much slower.

Based on the results of this work, the researchers discovered that the speed of color change is related to the distance the sodium atoms move.

PhD researcher Hannah Byron comments, "These observations are important for future material development, because we now know what is required of the host structure to allow control of the color-changing properties and their granularity."

"There were no characterization methods available to search for color-changing minerals, which is why we developed new methods ourselves," Lastosari says. "However, it is difficult to unambiguously interpret the results based on experimental data alone."

In fact, scientists could not reach current conclusions without strong support from theoretical calculations.

"We owe a lot of thanks for the collaboration of Professor Tanguy Le Bahers and his group, who developed computational methods suitable for such detail and precision that were not possible only a few years ago," Lastosari added.

Togtopite is a rare mineral that turns pink when exposed to ultraviolet rays (University of Turku)

Amazing App Capabilities

The Smart Materials Research Group at the University of Turku's Department of Chemistry, led by Lastusari, has long conducted pioneering research on materials with properties related to light and color, particularly on hackmanite.

"The strength of the color of the hackmanite depends on the amount of ultraviolet rays it is exposed to, which means that the material can be used, for example, to determine the UV index of the sun's radiation," Faury explains.

The hackmanite will be used on the space station in a similar way, but this feature can also be used in everyday applications.

For example, researchers have already developed a mobile phone application to measure UV radiation that anyone can use.

Researchers are currently developing many applications for Hackmanite. Instead of "LED" lamps and other light bulbs, they will replace natural minerals in X-ray imaging, dose detectors, and measure the radiation dose from materials that are absorbed during space flights to detect the negative aspects of the International Space Station.