Ask A Scientist General Science Archive

Question:  How do crystals form? ---Dave

Answer:
Crystals usually form from molten rock as the molten
rock gradually cools.  If the molten rock
cools very rapidly, then either small crystals
form or no crystals form.  An example of this
is when lava is ejected from a volcano.  If
molten rock cools slowly, then large crystals
can form.  This happens usually when the molten
material is very deep in the Earth.  Examples
of these types of crystals are diamonds, emeralds,
rubies, etc.
 
Crystals can also form when water evaporates.
For example, salt crystals (sodium chloride) form
when salt water evaporates.
 
The smooth faces of crystals are caused by
a regular internal arrangement of atoms.

-Grant