</ref>) are needed in order for snowflakes to form at temperatures above -40C. 85% of these nuclei are airborne bacteria, with dust particles making up the rest.<ref>Brenn, Max. [http://www.efluxmedia.com/news_Bacteria_The_Main_Ingredient_in_Snowflakes_Scientists_Say_14620.html Bacteria – The Main Ingredient in Snowflakes, Scientists Say]. ''eFluxMedia''. 29-02-2008.</ref> The ice crystals which form around the ice nucleators typically have a diameter of several milimetres and usually have six lines of symmetry. A snowflake is an aggregate of such ice crystals and may be several centimeters large<ref name="natgeojan07">{{Harvard reference | Surname=Klesius| Given=Michael| Title=The Mystery of Snowflakes| Journal=National Geographic| Volume=211| Issue=1| Year=2007| ID=ISSN 0027-9358|Page=20</ref>. The term "snowflake" is also used below for the symmetrical ice crystals themselves. The individual ice crystals are clear but because of the amount of light the individual crystals reflect snowflakes appear white in color unless contaminated by impurities.
Geometry
Image: SnowflakeSymmetry.jpg|thumb|left|Symmetry of an idealized snowflake
Image:LT-SEM snow crystal magnification series-3 frame.jpg|right|thumb|The first of a magnification series of a snow crystal (:Image:LT-SEM snow crystal magnification series-3.jpg|view the entire ser... read all