This book has crystals as well as other fun science challenges.
Answer:
A crystal is a solid in which the particles making up the crystal are packed in an ordered, repeated pattern.
Crystals form much like the forming of clusters of soap bubbles. In the diagram, the soap bubbles represent the particles in a crystal. The bubbles stack together forming a cluster. The addition of each bubble to the bubble cluster represents the stacking of particles in a crystal.
For information about the different ways that crystals form, see



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