Ask A Scientist Weather Archive

name         Henry
status       student
age          13

Question -   What are the types of snow crystals?
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Hi Henry!
Snow crystals generally have a hexagonal pattern, that present many beautiful external shapes. 
According to an international classification there are seven types of snow crystals, namely: 
plates; stellars; columns; needles; spatial dendrites; capped columns and irregular crystals. 
There are also three other types of solid precipitation that are called graupel, sleet and 
hail.
The size and shape of the snow crystals depend on the temperature of their formation and on the 
amount of water vapour present.
All these forms and shapes are conditioned by the internal arrangement in which the oxygen 
atoms form a network with the mentioned hexagonal symmetry.
Thanks for asking NEWTON!

Mabel
(Dr. Mabel Rodrigues)
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Henry,

The delicate feather-like snowflakes that appear to float rather than fall are actually 
pieces of ice.  They are most intricately patterned and consist of a great variety of hexagonal 
crystal forms.  An American photographer named Bentley was so fascinated by snow crystals that 
he amassed a collection of thousands of snow crystal photographs over a period of many years.  
He claimed that he never found two crystal alike.

The beginning of the six-sided ice crystal can be traced to the construction of the water 
molecule which consists of two atoms of hydrogen and one atom of oxygen (H2O).  This 
construction is formed in the shape of a triangle with three equal sides.  When 
crystallization takes place, each new ice-crystal bud is formed at an angle of 60 degrees 
from the hub or apex of the triangle.  Continuing this process, the hexagon is formed when 
six of these molecular triangles are completed.  As the crystal falls and is made larger by 
further sublimation and coalescence, its six-sided and six-angled form becomes the latticed 
framework for further growth and extension into several different basic crystal forms. These 
include columns, needles, flat planes, capped columns, stars and irregular groupings.

The above is excerpted from 1001 QUESTIONS ANSWERED ABOUT THE WEATHER by Frank H. Forrester, 
1981.

I hope this helps!

Sincerely,

Bob Trach
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Henry,

Technically, a snow crystal is defined as only one type of ice crystal, with a branched 
hexagonal (6 sided) shape.

However, there are many types of ice crystals, having a variety of shapes, including snowflakes 
(multiple crystals conglomerated together) and graupel (partially melted snowflakes that become 
little balls of snow).  Any of these falling from the sky are included in the precipitation 
called snow, even though they may not have the classic snow crystal form.

The various forms of ice crystals that can form in the atmosphere (including without clouds, if 
it is cold enough) include hexagonal columns and platelets (with no branches),  dendrites 
(with branches extending from a frozen water drop),  and ice needles (like a sewing needle; 
these are barely hexagonal and are the ones commonly seen falling from a  sky without clouds).

When ice columns or needles fall so that their long dimension is vertical, they can produce 
dramatic columns of light. A bright light on the ground is directed through the column of ice 
crystals and leaks out through the sides.  I have seen this most dramatically in the Arctic,
 but I have also seen it in Illinois and Kansas when it was very cold.  You may want to look 
 for these columns on a cold winter night.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
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