The largest snowflake has different growth patterns on the left and right branches. These branches are smaller, because they have had less access to water vapour due to the presence of the neighbouring snowflakes. This shows that at least those three crystals were partnered up for a while!
The lighter "rims" on the outer parts of the branches are also interesting. The same process that creates bubbles in snowflakes can cause "split ends". This happens when the top and bottom edge of a prism facet grow outward faster than the inside area. This leaves a cavity that can re-seal under certain conditions to create a bubble, or they can continue to grow out on two separate planes. The lighter area is caused but two layers of ice each reflecting back light to the camera. More reflective surfaces = more light reflected back.
Also interesting is the "capped column" in the lower right - probably the best example of this odd kind of snowflake formation I have seen to date! At certain temperatures, snowflakes grow into pillars of ice rather than "plates" like the other crystals in this image. If atmospheric conditions change, the growth can switch from one to another and sometimes back again, resulting in elaborate and unexpected designs.
Still have plenty of Sky Crystals books left in stock too. :) http://skycrystals.ca/