Snowflakes
For the basic facts about snowflakes and snow crystals, view and read through A Snow Crystal Primer by Kenneth G. Libbrecht from CalTech. You may also want to refer to the Snowflake Physics interactive primer from TeachersDomain.org or view it below.
Figure 5.2: In this interactive activity adapted from SnowCrystals.com, learn about snowflake formation and much more (requires Adobe Flash Playerto view). Animation from URL: http://www.teachersdomain.org/resource/lsps07.sci.phys.matter.snowflakes/