Scientists melted diamonds with a powerful laser to take some of the most precise measurements of the mineral’s elusive melting point, and found that previous experiments were off by more than 1,300 degrees Fahrenheit (700 degrees Celsius). It’s strange to think that diamond, the hardest natural material on Earth, is melting, but it does melt when shot with extremely powerful lasers under the right conditions. Understanding how diamond responds to laser shock waves is an important part of developing nuclear fusion, the process that powers stars. Nuclear fusion is also a potential source of energy for the future, so researchers have put a lot of effort into developing models that describe and predict how diamond behaves. However, the diamond is strange. Although experimental data and theoretical models agree fairly well most of the time, there have been some strange discrepancies that scientists have not been able to explain. The largest is the 2240 F (1244 C) difference, about 20%, between the above experimental data and the model-predicted diamond melting temperatures. There has also been some debate about whether diamond rearranges its atoms into a different type of solid carbon before becoming liquid at the end of the fusion process. Latest Videos from Live Science Researchers have struggled to explain these discrepancies because the conditions under which diamond is melted are so extreme that it is extraordinarily difficult to measure them in laboratories on Earth. However, new experiments may finally offer the solution scientists have sought for two decades. In a study published August 13 in the journal Nature Physics, scientists attacked small plates of synthetic diamond with an ultraviolet laser, creating shock waves so powerful that, as they passed through the samples, the diamond went from transparent to mirror-like. The sharp increase in reflectivity is an indication that the diamond was melted. By combining this change with measurements of how brightly the diamonds glowed while being attacked, the researchers mapped the melting temperature with great precision. “We were able to take small diamond samples and compress them to temperatures higher than the surface of the Sun and to pressures higher than the center of Neptune and Uranus, and still measure atomic structure, temperature, density and optical reflectivity,” study co-author Marius Millot, a research scientist at Lawrence Livermore National Laboratory in California, said in a statement. melting point in line with theoretical predictions and finally explaining the long-standing discrepancy. Get the world’s most fascinating discoveries delivered straight to your inbox. Artist’s concept of a solid piece of diamond floating in a puddle of metallic liquid carbon. The new experiment shows that this type of situation is possible deep on other planets. (Image credit: James Wickboldt/LLNL) The team also measured the atomic structure of the samples with X-ray diffraction and saw that the diamond did not transition to a different type of solid carbon before melting, possibly because the energy required to rearrange the atoms was too great, the researchers wrote. However, they also hypothesized that multiple shocks could be powerful enough for this transition to occur and that the way the shocks are applied to the diamond could affect how it changes phase. Understanding this is important for nuclear fusion research, since certain types of experiments involve lasers melting and crushing a diamond capsule to subject the capsule’s contents, solid deuterium and tritium, to more than 30 petapascals of pressure and temperatures above 180 million F (100 million C), the conditions necessary for a fusion chain reaction to occur. The researchers found that between about 660 and 1060 gigapascals of pressure and about 12,140 F (6,727 C), diamond exists as solid chunks floating in liquid carbon. As the pressure increases, more diamonds turn into liquid carbon, which is believed to be a very strange material. Unlike most forms of carbon on Earth (such as carbon, graphite, and diamond), liquid carbon is metallic, so it conducts electricity. It is also denser than diamond. So, hypothetically, if we were to somehow put liquid carbon in a cup without instantly vaporizing it, a chunk of solid diamond could happily float in it like an ice cube in a glass of water. Knowing how diamond behaves under such extreme conditions is also important for understanding the ice giant planets Uranus and Neptune. Based on measurements from the Voyager 2 spacecraft in the late 1980s and laboratory experiments on Earth, scientists believe that huge chunks of diamonds literally rain down into these planets and that their mantles may have oceans of liquid carbon with diamonds floating like icebergs. The new research means scientists can make better predictions about the interiors of planets and their carbon cycles. Millot, M., Coppari, F., Lazicki, A., Kim, Y., Landen, OL, Smalyuk, VA, Celliers, PM, and Eggert, JH (2026). Fusion of diamonds in shock compression experiments at pressures of 1 TPa. Nature Physics. https://doi.org/10.1038/s41567-026-03413-1 See how much you know about gemstones with our gold and gemstones quiz!
