It is fairly easy to grow your own crystal at home from lots of different substances and preserve it indefinitely. In the picture below, the Borax crystal is forming on a pipe cleaner in the shape of a snowflake. The pipe cleaner can be any shape and color, and you can even add food coloring. Borax crystals grow well on something submerged, as shown. Salt crystals, on the other hand, grow better from the bottom up (the salt crystal projects below are both Christmas tree shapes). Crystals are great projects for all ages and make great ornaments and sun catchers!
Growing a Borax crystal
Crystals are forms of solid matter that have ordered structures. Crystals often appear in a clearly geometric shape and many familiar things are crystals, including diamonds, graphite, salt, sugar, caffeine, and snow. Follow this link, or any other link in this post, for some information about crystals for kids.
Borax crystal structure from Chemistry.org
Borax is a naturally occurring substance that is great for cleaning and for growing your own crystals. Here are two links to Borax crystal projects:
http://chemistry.about.com/cs/howtos/ht/boraxsnowflake.htm
http://chemistry.about.com/od/holidayhowtos/a/Crystal-Snowflake-Ornaments.htm
You can also grow crystals using salt and bluing:
http://wemadethat.blogspot.com/2012/08/magic-tree.html
http://homechemistry.blogspot.com/2010/03/salt-crystal-trees.html
Here is a glow in the dark crystal project using Alum:
http://chemistry.about.com/od/crystalrecipes/a/glow-in-the-dark-alum-crystals.htm
And, you can grow a sugar crystal and EAT it:
http://video.about.com/candy/How-to-Make-Rock-Candy.htm
Crystals form when little bits of a substance (in this case: magnesium sulfate ions) arrange themselves in a regular pattern. Heating the water allows more Epsom salt to dissolve than could have in cold water. When the water cools, this extra salt is able to turn back into solid crystals. The pipe cleaner provides a location from which the crystals can start to grow.