Why the sky sparkles with ice crystals even on perfectly clear, sunny days

Nature · Published 3 October 2026 Swipe more like this →

In short: Diamond dust is a ground-level cloud of tiny ice crystals that glitters in the sunlight. Unlike fog, which is made of liquid water, this phenomenon forms directly as ice in freezing temperatures. It often appears under clear skies, creating a shimmering display that can baffle automated airport weather sensors.

Diamond dust, also known as ice mist or simply ice crystals, is a meteorological phenomenon that occurs when water vapor deposits directly into ice at the surface. Unlike fog, which consists of liquid droplets that may freeze later, diamond dust forms as solid, hexagonal ice plates or columns. Because these crystals are well-defined, they act like tiny prisms, reflecting and refracting light to create halos, sun dogs, and light pillars. The name originates from the visual effect of these crystals tumbling through the air, catching the sun and flashing like diamonds.

The formation of diamond dust typically requires a temperature inversion, where warmer air above mixes with colder air near the ground. This process increases the relative humidity of the surface air, allowing ice crystals to grow. While it can occur in any cold winter climate, it is most common in the interior of Antarctica, where temperatures frequently drop below −25 °C (−13 °F). In extremely clean environments lacking ice nuclei, water can remain liquid as supercooled droplets until temperatures reach about −39 °C (−38 °F), at which point they freeze into the crystals that constitute diamond dust.

The phenomenon is surprisingly persistent in polar regions. At Plateau Station in Antarctica, research indicates that diamond dust was observed on average 316 days per year. In 1967, it accounted for over 70% of the total precipitation recorded at the station, even though the total annual precipitation amounted to only 25 mm. While it is a natural occurrence, artificial diamond dust can also be generated by snow machines at ski resorts or by steam from manufacturing facilities. Because it is often thin, it may not significantly reduce visibility, though in some cases it can drop visibility to under 600 meters, occasionally causing automated weather stations to incorrectly report zero visibility.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Are those glowing pillars of light in the sky actually caused by diamond dust?
• Snow is made of clear ice, so why does it look white?
• Why that slushy mix falling from the sky is a meteorological balancing act
• Why freezing rain turns the world into a dangerous, transparent ice rink
• Earth's highest clouds shine at night because they are made of frozen space dust
• Why a volcanic eruption once triggered a surprising boom in global plant growth
• Can financial incentives turn the tide on the global loss of tropical forests?
• Two 1593 books from Manila are among the earliest printed works in the Philippines.
• How modern electronics manipulate direct current to power everything from phones to electric vehicles.
• How truck-mounted radar revolutionized our understanding of the most violent storms on Earth
• How one businessman once controlled a quarter of the Philippines' entire economic output
• Why the lightest rain might be the most powerful force in our climate

More in Air · More in Nature · Latest · A–Z · All topics