No two snowflakes are alike. Each one has its own distinctive formation. When it is snowing, the little white particles falling on our heads and into our mouths look alike.
There are seven different categories of snowflakes. There are approximately forty-one snowflake shapes. Most snowflakes follow geometric shapes. Many people think that snowflakes fall from freezing rain, but that is not true. Frozen rain is hail or sleet. It freezes as the rain comes out of the cloud.
Snowflakes begin in the clouds when water vapor condenses into ice. Patterns form as the crystals develop inside the clouds. The snowflakes vary according to saturation, and coldness. The hexagonal shapes start when the temperatures are at the freezing point and become more needle-like as the temperatures drop lower. In 1951, the International Commission on Snow and Ice developed a seven basic classification criteria. The following snowflake categories used the 1951 classification.
*Star Crystals are the most common of all snowflakes The temperatures for star crystals are -15degC.
*Stellar Dendrites are snowflakes that form an X with a line through it to make six arms. There are small branches that come off the main branch. They look like pine needles on a branch. They also remind one of a star in the sky. They form under extremely cold conditions. (-20 – 25degC)
*Irregular Crystals are the poor crystals that have bumped and hit different crystals. As a result, their structure is not distinguishable.
*Plates divide into different parts. These snowflakes lack moisture and do not develop the arms like star crystals do. They start by forming into a hexagon shape. After, they divide into six parts.
*Spatial Dendrites are ice crystals that mix together in a mishmash of shapes.
*Hollow Columns are hexagonal columns that are long, narrow and hollow.
*Rimed Crystals are similar to snowflakes. The water droplets freeze immediately inside the crystal.
*Needles look exactly like their name. They are long and shaped like columns that are thin. They form at lower altitudes and warmer temperatures. (-5 to -10 deg C)
*Simple Prisms are one-dimensional and small. They are hard to see because of their size.
*Capped Columns start off like hollow columns at higher altitudes but run into and connect to the star shape. These snowflakes are thicker than the column crystal, but few snow flakes are perfect.
Wind, temperature, altitude, and location are the final determinants of how a snowflake looks.
Source:
http://www.its.caltech.edu/~atomic/snowcrystals/class/class.htm
