Ice crystals

Close-up of a forming ice crystal.
Ice crystals on a frozen pond
Ice crystals
Ice crystals from cirrostratus making a circumzenithal arc in the sky
Dendritic ice crystals imaged with a scanning electron microscope. The colors are computer generated.

Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust.

- Ice crystals

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Cirrus cloud

Sky containing different types of cirrus clouds
A vast shield of cirrus clouds accompanying the west side of Hurricane Isabel
White cirrus in an anvil cloud
High cloud weather map symbols
Cirrus clouds merging to cirrocumulus clouds
Circumhorizontal arc
Heights of various cloud genera including high-, mid-, and low-level clouds
Large field of cirrocumulus clouds
Cirrostratus cloud
Cirrus clouds on Neptune, captured during Voyager 2 's flyby

Cirrus (cloud classification symbol: Ci) is a genus of high cloud made of ice crystals.


Water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 degrees Fahrenheit.

The three-dimensional crystal structure of H2O ice Ih (c) is composed of bases of H2O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).
Pressure dependence of ice melting
Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.
An alternative formulation of the phase diagram for certain ices and other phases of water
Frozen waterfall in southeast New York
Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F).
Ice on deciduous tree after freezing rain
A small frozen rivulet
Ice formation on exterior of vehicle windshield
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflakes by Wilson Bentley, 1902.
Harvesting ice on Lake St. Clair in Michigan, c. 1905
Layout of a late 19th-Century ice factory
Loss of control on ice by an articulated bus
Channel through ice for ship traffic on Lake Huron with ice breakers in background
Rime ice on the leading edge of an aircraft wing, partially released by the black pneumatic boot.
Skating fun by 17th century Dutch painter Hendrick Avercamp
Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

Liquid water is densest, essentially 1.00 g/cm3, at 4 °C and begins to lose its density as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached.

Diamond dust

Ground-level cloud composed of tiny ice crystals.

Halo display at the South Pole (1980), featuring a parhelion, 22° halo, parhelic circle, upper tangent arc and Parry arc. Diamond dust is visible as point-like reflections of individual crystals close to the camera.
Subhorizon halos in Ischgl: subsun, subparhelion and partial 22° halo, with the glint of ice crystals around the subsun.
Diamond dust briefly observed at Tsukuba, Japan. These are serial photos out of a movie; note differences in crystal locations.
Temperature was -2 °C, relative humidity was almost 100%. These photos captured only the glittering particles.

This meteorological phenomenon is also referred to simply as ice crystals and is reported in the METAR code as IC.

Ice fog

Bow River, Calgary Ice Fog at -20 °C, January 2015
Ice fog over Fairbanks, Alaska in winter 2005. Temperature approximately -30 F. Note the mirage at the base of the Alaska Range

Ice fog is a type of fog consisting of fine ice crystals suspended in the air.


Production of snow by forcing water and pressurized air through a "snow gun", also known as a "snow cannon".

Snow production at Camelback Ski Area, United States.
A graph of air temperature against relative humidity: if conditions are below the curve, snow can be made.
Pump house and air plant combination
Piping diagram
Snow lance used at Flottsbro in Stockholm
Parsenn ski resort compensating for low snowfall by producing artificial snow.
Figure 1. Average winter temperatures for the contiguous United States
Figure 2. Models trends in ski and snowboard resort revenues
A Water reservoir for snowmaking in the Stubai Alps

These products are organic or inorganic materials that facilitate the water molecules to form the proper shape to freeze into ice crystals.


Rare optical phenomenon of the halo family.

Anthelion (bottom) and 120° parhelion (top) depicted in Vädersolstavlan

Walter Tape, among others, has argued they are not separate haloes, but simply where various haloes caused by horizontally oriented column-shaped ice crystals coincide on the parhelic circle to create a bright spot.

Fractal curve

Magnified, that is, its graph takes the form of a fractal.

Construction of the Gosper curve
Zooming in on the Mandelbrot set

Fractal curves and fractal patterns are widespread, in nature, found in such places as broccoli, snowflakes, feet of geckos, frost crystals, and lightning bolts.

Milk substitute

Any substance that resembles milk and can be used in the same ways as milk.

A range of packaged plant milks from a Western grocery store.
Coffee-Mate, a synthetic coffee whitener made for use in coffee
Almond milk
Soy milk
Dairy-free ice cream
Infant formula

The preferred base for non dairy ice creams are often coconut milk or plant cream, due to the higher fat and lower water content preventing the formation of ice crystals.

Moon dog

Atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Moon.

Pair of moon dogs
Moon dogs appearing with a 22° halo around the Moon

Moon dogs are caused by the refraction of moonlight by hexagonal-plate-shaped ice crystals in cirrus or cirrostratus clouds.

Ice cave

Any type of natural cave that contains significant amounts of perennial (year-round) ice.

Dachstein-Rieseneishöhle in Austria
Ice plates
Needle ice extrusions

Although the portion of a cave within this permafrost zone will be below freezing, permafrost generally does not allow water percolation, so ice formations are often limited to crystals from vapor, and deeper cave passages may be arid and completely ice-free.