Look at the patterns in the balls in the gumball machine below. If you put identical marbles on a gently sloping flat tray, they will roll to the lower edge, and pack neatly together in the same way.
Spheres naturally fall into triangles, which form hexagons,
with six spheres surrounding each sphere. Wherever you look, order is natural,
at least in solids made of identical particles.
Crystals form because atoms are real,
identical objects that pack neatly. Crystals form regular shapes, so they must
be made of identical tiny units. Crystals get flat edges because wandering
particles are more likely to stick to a gap that is filled on two or three
sides. Once they stick in place, they are less likely to be knocked off again
(unlike the corners and stick-out bits), so the gaps in crystals are filled in
first, and the crystals develop flat sides.
Water
crystals
Higher-latitude Americans and northern Europeans know all
about ice crystals, because they see snow every year, but few Australians live
in alpine conditions.
With just a
camera, a coffee jar, a damp cloth, a microwave and a freezer, you can make
imitation snow crystals. Put a few drops of water in the jar, put the lid on
but leave it loose (think about why!) and give the jar 20 seconds on high in
the microwave to warm the water inside, then put a lid on it tightly, and leave
the jar in the freezer overnight.
Next day, there will be tiny ice crystals inside the jar, where the water vapour has frozen on the glass. The crystals won’t last long, so unless you live in a cold climate, you need help and a foam box with ice bricks to carry them to a bright spot to photograph them. The crystals look like this:
Water crystals.
Water vapour from the air condenses on the outside of the
jar as soon as it comes out of the freezer, so you need a damp cloth to wipe
the glass dry.
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