Grow Sugar Crystals (Rock
Candy) 
Crystals are found in snowflakes, diamonds and rubies, gold, the
graphite used in pencils, and table salt. In fact, crystals are found in
most non-living substances and 70 per cent of the earth’s solid crust
is crystalline.
A crystal is made up of millions of atoms sequenced in a pattern that is
repeated throughout the entire crystal. A magnifying glass will reveal
that
salt crystals are cubelike, with flat sides. In contrast, sugar
crystals
are
oblong and sharply slanted at either end.
Almost all cut gems begin in the crystalline form before being faceted
and
polished to heighten their beauty. This project will allow you to create
colourful crystals good enough to eat.
Materials
1000 mL (4 cups) sugar
250 mL (1 cup) water
String, pencil, and paper clip.
Pyrex measuring cup
Saucepan and spoon
Food colouring
Magnifying glass (optional)
Instructions
Heat water in a saucepan and stir in half the sugar until dissolved.
Add
the
remaining sugar and continue to heat until solution is clear.
Carefully pour solution into a Pyrex measuring cup. Add several drops of
food colouring.
Tie one end of the string to the pencil; attach the paper clip to the
other
end. Place the pencil across the top of the cup and allow the string to
dangle. Avoid shaking or touching. Put the cup somewhere it won't be
disturbed.
A warm place with no vibrations (not on top of the refrigerator) will
work
best.
The slower the solution cools, the bigger the crystals will get.
Sugar crystals will be large enough to eat in several days. You may want
to study the crystal formation with a magnifying glass.
The same experiment can be done with salt crystals. Salt will make
crystals
of a
different shape. Every chemical forms its own, distinctive crystals.
Impurities
(like the food coloring) are usually what gives natural mineral
crystals
their
colors.
Mineral crystals form from solutions deep underground that are from
around the boiling point of water up to hundreds of degrees. These high
temperatures
for water solutions are possible because the water is trapped under
high
pressures
in cracks and gas bubbles in the rocks. If the water had a way out, it
would turn instantly
to steam and vent above ground, as a geyser does.