Microscopes and Crystals - National High Magnetic Field Laboratory

ACTIVITY 15: WHAT VARIABLES AFFECT CRYSTAL GROWTH?
m6: Microscopes and Crystals
A CT
A
CTIVITY
What Variables Affect Crystal Growth?
lmost every solid that occurs in nature is made up of
crystals. The minerals found on earth have differently shaped
crystals. Salt looks like rough sand to the unaided eye, however
when viewed through a magnifying glass or a microscope, it
is actually made up of small cube-shaped crystals. Many
crystals are transparent; others are colored. Some crystals,
like salt are very small, while others are large enough to be
seen without a hand lens or a microscope.
Some crystals are formed when molten rock cools and hardens.
Others are formed when water containing dissolved minerals evaporates. In both cases, the
atoms of the minerals form solids by coming together in regular repeating patterns. (See Activity
14) These repeating patterns make crystals both strong and hard. Crystals of the same mineral
always follow the same growth pattern.
In this activity, students will design investigations about crystals. If they are trying to find out
how different variables affect crystal growth, they need to first identify the variables they will
be studying. There are two types of variables, manipulated and responding variables. If a
variable is deliberately changed it is called a manipulated variable. The variable that may
change as a result of changing the manipulated variable is called the responding variable. Students
in this activity are going to investigate how variables affect crystal growth.
MATERIALS:
! Baby food jars, clear film canisters, or other containers
! Water (some warm, and some at room temperature)
! Measuring spoon (1 tsp = 5 ml)
! Copper Sulfate (CuSO 4
), Epsom salt, table salt, sugar, borax or other crystal-forming
substance
! Slides
! Droppers or straws
! Field microscope
! Science Notebooks
! Hand lens
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