Hint: Hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust are examples of ice crystals that show atomic ordering on different length scales. Ice crystals form cirrus clouds in the free air and the hydrometeor known as "ice crystals" near the ground.
Complete answer: Water molecules, which are made up of two hydrogen atoms and one oxygen atom, make up ice crystals. From the atomic nucleus, the two hydrogen atoms form a $104.5$- degree angle. Since the oxygen atom absorbs more electrons, the water molecule is slightly negative on one side and slightly positive on the other. As bipolar molecules in water freeze, they attract each other and form a hexagonal crystal lattice. Water molecules cannot deposit haphazardly onto ice crystals as they grow. The molecules must fit into the crystal's form. The habit of a crystal refers to its form. The crystal habit is determined by the temperature and vapour content of the atmosphere. Temperature and humidity change as the crystal passes through the atmosphere, changing the growth habit and resulting in very complex shapes. The crystal's final form would be determined by the environmental conditions it encountered as it travelled through the atmosphere. Water molecules are the basic particles that form ice crystals. It's a molecular crystal, to be precise. The water molecules are organised in an ordered sequence in a cage-like structure, resulting in a crystalline structure. Crystalline compounds are made up of particles or molecules that are arranged in a particular order, such as ice particles or water molecules, to form an ordered structure.
Note: When people say "snowflake," they're usually referring to a snow crystal. The above is a single ice crystal in which all of the water molecules are arranged in a hexagonal pattern. The six-fold symmetry of snow crystals is something we're all familiar with.